<webview>: Expose transparency API

BUG=157628

Review URL: https://codereview.chromium.org/95693002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238428 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238428
Adds unit tests for swipe flick. We add the following tests:
1) Regular swipe flick (Should type hintText)
2) Long swipe flick (Nothing should display)
3) Composed swipe followed by flick (moveCursor triggered, but no flick)


BUG=324823

Review URL: https://codereview.chromium.org/99923003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238429 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238429