Add support for SubpixelFontScaling flag on windows

Implement support for the SubpixelFontScaling runtime enabled feature
on windows.

BUG=290411
R=pdr@chromium.org

Review URL: https://codereview.chromium.org/25639003

git-svn-id: svn://svn.chromium.org/blink/trunk@158966 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Clear MediaController::m_scriptExecutionContext when the ScriptExecutionContext is destroyed

HTMLMediaElement is an ActiveDOMObject, so it's possible that HTMLMediaElement
outlives ScriptExecutionContext. Hence the HTMLMediaElement has to clear out
the ScriptExecutionContext of MediaController that the HTMLMediaElement owns.

Review URL: https://codereview.chromium.org/25989002

git-svn-id: svn://svn.chromium.org/blink/trunk@158967 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Move SecureTextInput.cpp/.h to Source/platform/

BUG=297477

Review URL: https://codereview.chromium.org/25541007

git-svn-id: svn://svn.chromium.org/blink/trunk@158968 bbb929c8-8fbe-4397-9dbb-9b2b20218538