cc: Improve worker pool performance by using std:make_heap instead of std:priority_queue.

cc: Improve worker pool performance by using std:make_heap instead of std:priority_queue.

This reduces the complexity of building a new "ready to run" queue in
WorkerPool::SetTaskGraph() from O(N·log(N)) to O(N).

This refactor is also useful for supporting shared worker threads as it
makes it easy to reuse the compare function and maintain a heap of
ready to run task namespaces.

BUG=246546
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=242833

[vmpstr, 2014-01-02 05:09:44]

lgtm, thanks!

[commit-bot: I haz the power, 2014-01-02 05:28:38]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/reveman@chromium.org/123113002/1

[commit-bot: I haz the power, 2014-01-02 23:23:08]

Change committed as 242833