Fixed html select drop downs appearing underneath always-on-top windows and panels

Always-on-top app windows and docked panels have the WS_EX_TOPMOST bit
enabled. The dropdown of any SELECT elements contained in the window
are top level windows without WS_EX_TOPMOST set, making them appear
below the window.

This patch makes the dropdowns topmost windows if the root windows are
topmost.

BUG=334427
TEST=See bug for sample extensions and apps to reproduce and verify.

Review URL: https://codereview.chromium.org/139343003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246553 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246553
Re-land: cc: Remove WorkerPool class and instead use TaskGraphRunner directly.

Removes the unnecessary WorkerPool layer. This makes the job
of the TaskGraphRunner more clear and will allow us to remove
some complexity and unnecessary heap allocations from the
RasterWorkerPool code in follow up patches.

Also moves the kNumRasterTasks switch to content/.

Refactor only, no changes in behavior.

BUG=331844

Review URL: https://codereview.chromium.org/141163019

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246554 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246554