In the tabs section of the gallery, the beach ball can get in a state where it sits slightly under the header. The resting state should be sitting fully underneath the header.

Steps to Reproduce

• Build and install latest Flutter Gallery from the repo, enter "Tabs" section,
• scroll "Left" section to the bottom,
• select to "Right" tab,
• Notice that the beach ball is scrolled under the header a little bit, and will sit there.

Flutter Doctor

[✓] Flutter (on Mac OS X 10.12.4 16E195, locale en-US, channel master)
• Flutter at /Users/KG/Developer/Flutter/flutter
• Framework revision 37e32d5 (21 hours ago), 2017-06-12 12:23:13 -0700
• Engine revision ffe8181
• Tools Dart version 1.24.0-dev.6.7

[✓] Android toolchain - develop for Android devices (Android SDK 25.0.3)
• Android SDK at /Users/KG/Library/Android/sdk
• Platform android-25, build-tools 25.0.3
• ANDROID_HOME = /Users/KG/Library/Android/sdk
• Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
• Java version OpenJDK Runtime Environment (build 1.8.0_112-release-b06)

[✓] iOS toolchain - develop for iOS devices (Xcode 8.3.3)
• Xcode at /Applications/Xcode.app/Contents/Developer
• Xcode 8.3.3, Build version 8E3004b
• ios-deploy 1.9.1
• CocoaPods version 1.2.1

[✓] Android Studio (version 2.3)
• Android Studio at /Applications/Android Studio.app/Contents
• Gradle version 3.2
• Java version OpenJDK Runtime Environment (build 1.8.0_112-release-b06)

[✓] IntelliJ IDEA Community Edition (version 2017.1.4)
• Flutter plugin version 14.0
• Dart plugin version 171.4694.29