Add support for horizontal mouse wheel messages in Windows Desktop Aura.

This is simply a matter of recognizing the WM_MOUSEHWHEEL message as a valid mouse wheel message.
Tested this on web pages with horizontal scrollbars and it works well.

BUG=332797
R=sky@chromium.org, sky

Review URL: https://codereview.chromium.org/140653006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245651 0039d316-1c4b-4281-b951-d872f2087c98
Clicking on the body or the action buttons closes synced notifications.

This reverts r231502 back to the previous behavior, no new code
changes.

BUG=333347

Review URL: https://codereview.chromium.org/132233013

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245652 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245652
sync: Introduce ModelTypeRegistry and helpers

Introduce the ModelTypeRegistry class and use it to manage the creation
of UpdateHandlers and CommitContributors.  The ModelTypeRegistry also
gets some help from the newly introduced UpdaterList and CommitterList
classes.

This lets us move the verbose iteration logic out of the code that's 
focused on building and executing commits and updates, which should make 
those functions easier to read. It gives us more freedom to experiment 
with other ways to manage the lists of commit contributors and update 
handlers, should we choose to do so. It prevents us from leaking the 
set of enabled types through the per-type maps. 

This patch is one of the last in the stack related to building a 
per-type abstraction into the sync engine, and also one of the first 
steps towards implementing run-time enable and disable logic for the 
new-style sync types. 

BUG=278484

Review URL: https://codereview.chromium.org/93433006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245654 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245654