As part of the extensions module refactor we temporarily allowed the use
of chrome_notification_types.h in src/extensions. However, this allowed
code moving into src/extensions to listen to notifications from Chrome,
which was a layering violation.
This CL moves all the extensions notifications into their own header and
cleans up DEPS to disallow the exception.
BUG=392622
TEST=compiles, unit_tests, browser_tests, extensions_unittests
TBR=miket@chromium.org for apps/
Review URL: https://codereview.chromium.org/425303002
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@286770 0039d316-1c4b-4281-b951-d872f2087c98
adf5a10eeb