Add "Inspect Element" shortcut to browser tabs.

If the DevTools window is closed, it gets opened, and the Inspect Element tool is enabled. If the DevTools window is opened, the inspected tab remains focused with the Inspect Element tool enabled.
If the Inspect Element tool is enabled, it gets turned off.

The shortcut is Ctrl-Shift-C for Win/Linux, Cmd-Shift-C for Mac

BUG=29532
TEST=manual

Review URL: http://codereview.chromium.org/3011002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@52651 0039d316-1c4b-4281-b951-d872f2087c98
16 files changed