Track extension resource timestamp deltas

This adds stats to examine the deltas between the modification time
of extension resources on the filesystem and the creation time
of their extension's root directory.

Review URL: https://codereview.chromium.org/62873004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235470 0039d316-1c4b-4281-b951-d872f2087c98
Send ChromeViewMsg_SearchBoxToggleVoiceSearch IPC message from SearchIPCRouter.

Clean up SearchIPCRouterTest and SearchIPCRouterPolicyTest along the way.

BUG=272583
TEST=none

Review URL: https://codereview.chromium.org/67293003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235471 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 235471