• VSCode Version: 1.3.0-insider
• OS Version: windows7

Steps to Reproduce:

1. Download My extension: https://github.com/f111fei/test-files/raw/master/webview-test-0.0.1.vsix
2. Run command Hello Webview to open my webview.

Problem:

1. Drag Button into TextArea. Dragfeedback overlay will prevent my dragging action.
2. Typing some text in the textarea. Use Ctrl+A to select all, Nothing happen.

Reason

1. see https://github.com/Microsoft/vscode/blob/master/src/vs/workbench/electron-browser/window.ts#L91, the default drag handler is prevented.
2. see https://github.com/Microsoft/vscode/blob/master/src/vs/platform/keybinding/browser/keybindingServiceImpl.ts#L380, selectAll handler is prevented.