Revert of Don't peek messages in the MessagePumpForUI class when we receive our kMsgHaveWork message.

Revert of Don't peek messages in the MessagePumpForUI class when we receive our kMsgHaveWork message. (patchset #2 id:20001 of https://codereview.chromium.org/1194673004/)

Reason for revert:
Causes one 1 task to run per 3 ms when in a nested modal loop, which causes resize to lag behind.

BUG=505612
Original issue's description:
> Don't peek messages in the MessagePumpForUI class when we receive our kMsgHaveWork message.
> Relanding this patch with fixes for the performance issues reported with the worker thread hogging the CPU continuosly. (https://codereview.chromium.org/1181263008/)
>
> Currently the MessagePumpForUI class peeks Windows messages when we receive the kMsgHaveWork message in
> our main message loop and in nested modal loops. This is because the posted message starves the message loop
> of input and other lower priority messages. While this is ok for the main message loop our peeking and dispatching
> messages in nested loops is wrong and violates the silent contract where in the nested loop should be the one peeking
> and dispatching messages.
>
> To fix this the approach we are taking is to create a worker thread which uses a waitable timer of 3 ms which posts
> the kMsgHaveWork message to the main loop when the timer fires. As a result we can safely delete all the code
> in the MessagePumpForUI::ScheduleWork function and simplify the ProcessPumpReplacementMessage function.
>
> The MessagePumpForUI::ScheduleWork function now checks the delay for the task at the head of the queue
> If it is 0 then we post the message right away as it is a regular task. Added functions (GetNewlyAddedTaskDelay) to the MessagePump::Delegate class and the IncomingTaskQueue for this.
>
> The other change here is to change the GPU process to use the IO message pump by default and use the UI pump only
> if we are using opengl. Reason being this patch causes a delay in processing tasks due to the worker thread which
> causes tests like webgl_conformance to fail. We will continue working on addressing this over the coming days.
>
> To prevent the UI worker thread from continuously posting the timer we use a flag to control the same.
> The flag ensures that the worker thread posts the timer once for each iteration.
>
> This patch also contains a fix for the crash reported in bug 501602 which occurs due to the GetNewlyAddedTaskDelay
> function being called from the WndProc which does not have the incoming queue lock. Fix is to move some of the
> logic in the ScheduleWork function to the newly added ScheduleWorkHelper function.
>
> BUG=492837, 501602
> TBR=cpu
>
> Committed: https://crrev.com/4d5496cde5b81436954e31a9fe82e35ccfe5de49
> Cr-Commit-Position: refs/heads/master@{#335475}

TBR=scottmg@chromium.org,cpu@chromium.org,brucedawson@chromium.org,kbr@chromium.org,ananta@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=492837, 501602
Committed: https://crrev.com/ca6bfb547d1ee58459b06ab79dd87a0f14081f4c
Cr-Commit-Position: refs/heads/master@{#337113}

[jbauman, 2015-07-01 21:16:08]

Created Revert of Don't peek messages in the MessagePumpForUI class when we
receive our kMsgHaveWork message.