Add histograms to record document.execCommand.

The user metrics was introduced at 
https://src.chromium.org/viewvc/blink?view=rev&revision=165849.

Each value is from an array definition in WebKit/Source/core/editing/EditorCommand.cpp.
If you edit the array, you should run update_editor_commands.py to update histograms.xml validly.

BUG=338241

Review URL: https://codereview.chromium.org/142713003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254423 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254423
Enable user policy for Kiosk App sessions.

This enables user policy to take effect in Kiosk App sessions. It's
currently using the standard user policy protobuf in the backend as is
used for Public Sessions. We may want to change that once Kiosk Apps
get handled by app_shell.

BUG=chromium:333434

Review URL: https://codereview.chromium.org/181383003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254424 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254424