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Based on Windows folks reply, this scroll lagging issue is because the
message hit test to wrong window (Intermediate D3D Window) and need to
forward to the correct window (Chrome Legacy Window), but Chrome Legacy
Window is holding the input queue lock so Intermediate D3D Window can
not forward the message.

This fix adding 3 window extended styles to Intermediate D3D Window:

WS_EX_LAYERED | WS_EX_TRANSPARENT | WS_EX_NOREDIRECTIONBITMAP

The first two should make the window transparent for input, and the
third avoids allocating a bitmap that would otherwise be allocated with
WS_EX_LAYERED.

WM_PAINT, WM_ERASEBKGD and ClearInvalidContents() also removed because
they unnecessary for transparent layered window.

Bug: 871257
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: Ic708b4d2a5a37f8e2e98e425c1be8b28de41d001
Reviewed-on: https://chromium-review.googlesource.com/c/1299342
Commit-Queue: Jianpeng Chao <chaopeng@chromium.org>
Reviewed-by: Sunny Sachanandani <sunnyps@chromium.org>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603073}