Fix a page responsive dialog showing up in Chrome Desktop Windows Aura if we hovered or clicked on the portion of the window
where the OS thinks that there is a native scrollbar.

We fake the scrollbar styles on top level windows in Chrome Windows Desktop Aura to ensure that trackpoint and trackpad
scrolling works. We hide the Windows scrollbars to ensure that we don't see two scrollbars on the window, one drawn by Webkit
and one by Windows.

If we hover/click on the area of the window where the scrollbars would be drawn, the default WM_NCHITTEST returned by the OS
is HTVSCROLL or HTHSCROLL. This then results in non client mouse messages being delivered to the renderer which does not ack them
leading to the dialog showing up.

As we dont't have Windows native scrollbars in Windows Desktop Aura, we can safely return HTCLIENT for these hittests. I gave a local build to QA to test. Worked fine
with the following tests
1. Inspector popped in and out of Chrome
2. Page resizing, tab dragging, etc.
3. Task manager, bookmark tree view

This change should not cause any major fires. If it does, will consider reverting the scrollbar hack and look into another approach.

BUG=335248
R=cpu@chromium.org
TBR=sky

Review URL: https://codereview.chromium.org/131743025

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245681 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245681