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::PeekMessage can process sent-messages and internal events. It seems
the kernel also uses it as a heuristic to deschedule the main thread when
it thinks it's out of messages. In MessagePumpForUI's design, it's
possible to have application tasks without pending native tasks
(kMsgHaveWork is dropped when running out of native tasks).

This CL uses ::GetQueueStatus() to probe the presence of messages before
invoking ::PeekMessage().

Bug: 1075960
Change-Id: I4a93b22adf225ae2d62aabeb1a7a734232cf7fb6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2258456
Auto-Submit: Gabriel Charette <gab@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Commit-Queue: François Doray <fdoray@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#781498}