Relanding this as the previous attempt failed on linux aura

Perform the window activation code in WM_ACTIVATE instead of WM_NCACTIVATE.

This ensures that we don't inadvarently mark a window as active when the code uses APIs like FlashWindow,
which send periodic WM_NCACTIVATE messages to flash the caption.

BUG=297813
TEST=Covered by ui test WidgetNotActivatedOnFakeActivationMessages
TBR=sky@chromium.org

Review URL: https://codereview.chromium.org/25131002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225851 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225851