[Omnibox] Add UMAs to track copy/paste operations.

R=pkasting@chromium.org
BUG=316236

Review URL: https://codereview.chromium.org/65113005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235874 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 235874