Fix the 17px dead region in the bottom right corner of top level browser windows.

Fix the 17px dead region in the bottom right corner of top level browser windows.

This is a sideeffect of the fake WS_VSCROLL and WS_HSCROLL styles added to the window and us hiding the scrollbars
during sizing operations.

Bug does not exist on Windows 8. On Windows 7 hovering near the bottom right portion of the window where the vertical
scrollbar would be returns HTBOTTOMRIGHT instead of HTVSCROLL or HTHSCROLL which we already handle. This eventually results
in non client mouse messages like WM_NCMOUSEMOVE/WM_NCMOUSEDOWN being sent to the RWHA window which are ignored.

Attempted fix is to check in WM_NCHITTEST if the mouse coordinates are in the bottom portion of the window using metrics
like SM_CXVSCROLL/SM_CYVSCROLL/SM_CXSIZEFRAME/SM_CYSIZEFRAME and if yes convert the hittest code to HTCLIENT.

BUG=335487
R=sky@chromium.org, sky

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=247584

[sky, 2014-01-28 23:58:19]

LGTM - I wonder if there are any high dpi issues here (feel free to ignore for
now).

[ananta, 2014-01-29 01:56:55]

Committed patchset #3 manually as r247584 (presubmit successful).