Move Editor::interpretKeyEvent to EditingBehavior.
We will change the platform depending implementation from the #ifdef style to EditingBehaviorType.

BUG=N/A

Review URL: https://codereview.chromium.org/100873003

git-svn-id: svn://svn.chromium.org/blink/trunk@164000 bbb929c8-8fbe-4397-9dbb-9b2b20218538