A bit of cleanup for the Extension Commands.

Adding namespace extensions for ExtensionKeybindingRegistry, and renamed Extension::Keybinding to Extension::Command.

BUG=None
TEST=None (no code change).
Review URL: https://chromiumcodereview.appspot.com/10298013

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@135313 0039d316-1c4b-4281-b951-d872f2087c98
16 files changed