iOS: Eliminate the Impeller/Skia backend selection params - #190416

…lutter#190509)

This relands flutter#190419, which I reverted in flutter#190501 because it broke the
tree due to a (non-merge) conflict with flutter#190416.

flutter#190419 added a local `FakeIOSContext` whose `GetBackend()` override
returned `flutter::IOSRenderingBackend::kImpeller`.

flutter#190416 landed immediately before it and removed the
`IOSContext::GetBackend()` virtual and the `IOSRenderingBackend` enum,
so the two changes had no merge conflicts but `FakeIOSContext` no longer
compiled once both were in the tree.

This reland is identical other than deleting the `GetBackend()`
override. `FakeIOSContext` still inherits the null Impeller/Aiks
contexts from the base class and returns no external texture, matching
the behaviour the tests rely on.

Original change:

`FlutterPlatformViewsTest` used the internal engine class
`flutter::IOSContextNoop` in a dozen places purely as a no-op context to
hand to `submitFrame:withIosContext:`. This replaces those with a local
`FakeIOSContext` that replicates the behaviour the tests rely on so that
we can delete `IOSContextNoop` in a follow-up.

Back in ancient times, before the simulator required Metal, and when iOS
still had a Skia software renderer, we ran that on the Simulator due to
some issues with our OpenGL implementation. Later, Flutter on iOS
migrated from Skia to Impeller. Skia supports a software backend but
Impeller did not, and so when running on Impeller, we stubbed out the
software backend to no-op context/surfaces, hence IOSContextNoop and
IOSSurfaceNoop. The Simulator now *requires* Metal and Flutter has
eliminated Skia support altogether so there's no longer a software mode
at all, nor a need for a no-op path in case you're using Impeller and
ask for a software backend.

This is part of a series of changes to remove the dead no-op fallback.

No behavioural change; just a test refactoring.

Issue: flutter#190041

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…12406)

Manual roll Flutter from e52f01c920ad to b766512c65d8 (42 revisions)

Manual roll requested by [email protected]

flutter/flutter@e52f01c...b766512

2026-08-04 [email protected] Roll Dart SDK from 2a799a2404e9 to 9859c0a39adb (4 revisions) (flutter/flutter#190521)
2026-08-04 [email protected] Revert: iOS: Eliminate use of IOSContextNoop in platform view tests (flutter/flutter#190501)
2026-08-04 [email protected] [Impeller] Enable ETC2/ASTC LDR/BC texture compression features at Vulkan device creation (flutter/flutter#189303)
2026-08-03 [email protected] Remove openglessdf from impeller_unittests. (flutter/flutter#190469)
2026-08-03 [email protected] [web] Unify image decoding and codecs on CanvasKit and Skwasm (flutter/flutter#188573)
2026-08-03 [email protected] iOS: Eliminate use of IOSContextNoop in platform view tests (flutter/flutter#190419)
2026-08-03 [email protected] Add path rendering benchmarks (flutter/flutter#188654)
2026-08-03 [email protected] Add windows platform support for primitive_shape_test integration test (flutter/flutter#190464)
2026-08-03 [email protected] Roll Skia from 958c1c1921a1 to a08d918ebd6a (3 revisions) (flutter/flutter#190467)
2026-08-03 [email protected] tests: add --ios-runtime param (flutter/flutter#190414)
2026-08-03 [email protected] iOS: Remove the synchronous first-frame wait (flutter/flutter#190432)
2026-08-03 [email protected] iOS: Eliminate the Impeller/Skia backend selection params (flutter/flutter#190416)
2026-08-03 [email protected] iOS,macOS: Use @autoclosure in Logger (flutter/flutter#190417)
2026-08-03 [email protected] tools: Support FLUTTER_HOST_ARCH in update_dart_sdk scripts (flutter/flutter#190421)
2026-08-03 [email protected] iOS: Hardcode rendering API to Metal in tests (no-op) (flutter/flutter#190422)
2026-08-03 [email protected] a11y: Map disabled/read-only semantics to AX node restriction (flutter/flutter#190353)
2026-08-03 [email protected] [Infra] Replace defunct umbrella template with Wasm issue form (flutter/flutter#190471)
2026-08-03 [email protected] Roll Skia from abecb0dc02c1 to 958c1c1921a1 (4 revisions) (flutter/flutter#190459)
2026-08-03 [email protected] Roll Dart SDK from 65b163be2485 to 2a799a2404e9 (3 revisions) (flutter/flutter#190454)
2026-08-03 [email protected] Roll Skia from 68efb3f2ad16 to abecb0dc02c1 (1 revision) (flutter/flutter#190443)
2026-08-03 [email protected] Roll Packages from 5351d8c to ac87e65 (4 revisions) (flutter/flutter#190441)
2026-08-03 [email protected] Roll Skia from 5a761eb826c1 to 68efb3f2ad16 (1 revision) (flutter/flutter#190440)
2026-08-03 [email protected] Roll Skia from 4c9f8b4805e2 to 5a761eb826c1 (1 revision) (flutter/flutter#190437)
2026-08-03 [email protected] [macOS] Resume app lifecycle on becomeActive to avoid frozen UI after occlusion (flutter/flutter#188772)
2026-08-03 [email protected] Roll Skia from 39cda9d6d7d2 to 4c9f8b4805e2 (6 revisions) (flutter/flutter#190426)
2026-08-03 [email protected] Roll Skia from df13bfb5a54e to 39cda9d6d7d2 (2 revisions) (flutter/flutter#190425)
2026-08-02 [email protected] iOS: Serialise CADisplayLink access in VSyncClient tests (flutter/flutter#190335)
2026-08-02 [email protected] Roll Skia from 32329e5643b5 to df13bfb5a54e (1 revision) (flutter/flutter#190394)
2026-08-02 [email protected] [Impeller] Skip binding dead-code-eliminated resources on Metal (flutter/flutter#190040)
2026-08-01 [email protected] [Flutter GPU] Raise Dart errors for invalid render pipelines and memoize per-draw pipeline state (flutter/flutter#189899)
2026-08-01 [email protected] Revert "Improve non rect platform view rendering  (#182662)" (flutter/flutter#190003)
2026-08-01 [email protected] Roll Skia from ebf50520d720 to 32329e5643b5 (1 revision) (flutter/flutter#190389)
2026-08-01 [email protected] Roll Skia from f73c4510d12d to ebf50520d720 (6 revisions) (flutter/flutter#190376)
2026-07-31 [email protected] Primitive shape integration test (flutter/flutter#190368)
2026-07-31 [email protected] Eliminate some early returns in uber_sdf.frag to fix broken UberSDF AA on Windows (flutter/flutter#190260)
2026-07-31 [email protected] chore: swiftshader mirrored + llvm16 (flutter/flutter#181225)
2026-07-31 [email protected] [web] Remove in-repo agent documentation (flutter/flutter#190326)
2026-07-31 [email protected] [windows]: Uses offscreen MSAA when implicit msaa isn't available. (flutter/flutter#190256)
2026-07-31 [email protected] flutter_tools: Use new FileSystemExtension from devtools (flutter/flutter#190360)
2026-07-31 [email protected] Roll Dart SDK from c3acfc2479f6 to 65b163be2485 (1 revision) (flutter/flutter#190358)
2026-07-31 [email protected] Use devicectl for screenshots on Xcode 27, remove idevicescreenshot artifact (flutter/flutter#189091)
2026-07-31 [email protected] Roll Skia from 7ef86a5b0eb9 to f73c4510d12d (1 revision) (flutter/flutter#190352)

If this roll has caused a breakage, revert this CL and stop the roller
...