Chromium side of moving clearContextMenu from WebViewClient to WebFrameClient.

BUG=304341
R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/177923011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255479 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255479