Fix DCHECK during TileManager shutdown

Fix DCHECK during TileManager shutdown with ImageRasterWorkerPool

DCHECK_EQ(0u, tiles_.size()) in TileManager destructor can fail because
refs to tile could exist through |root_| WorkerPoolTask in
WorkerPool::Inner. Fix by calling ScheduleRasterTasks with emtpy
RootTask in ImageRasterWorkerPool::ShutDown.

BUG=

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=205510

[boliu, 2013-06-09 00:25:36]

I was playing around with webview using mapped image and saw this DCHECK. This
appears to fix it.

I wonder if this is a mapped image only bug though. I don't think I have seen
this DCHECK while using pixel buffer mode (didn't test it much). There is
PixelBufferRasterWorkerPool::Shutdown => CheckForCompletedRasterTasks =>
ScheduleMoreTasks => which may have set root_ to null on shutdown?
ImageRasterWorkerPool does not override Shutdown and I don't think root_ could
have been released anywhere else.

Should the fix be in ImageRasterWorkerPool?

[reveman, 2013-06-10 16:04:36]

On 2013/06/09 00:25:36, boliu wrote:
> I was playing around with webview using mapped image and saw this DCHECK. This
> appears to fix it.
> 
> I wonder if this is a mapped image only bug though. I don't think I have seen
> this DCHECK while using pixel buffer mode (didn't test it much). There is
> PixelBufferRasterWorkerPool::Shutdown => CheckForCompletedRasterTasks =>
> ScheduleMoreTasks => which may have set root_ to null on shutdown?
> ImageRasterWorkerPool does not override Shutdown and I don't think root_ could
> have been released anywhere else.
> 
> Should the fix be in ImageRasterWorkerPool?

Thanks for tracking this down. Yea, can you implement
ImageRasterWorkerPool::Shutdown() and call ScheduleRasterTasks(RootTask()) after
RasterWorkerPool::Shutdown()?

[boliu, 2013-06-10 22:20:09]

On 2013/06/10 16:04:36, David Reveman wrote:
> Thanks for tracking this down. Yea, can you implement
> ImageRasterWorkerPool::Shutdown() and call ScheduleRasterTasks(RootTask())
after
> RasterWorkerPool::Shutdown()?

Done

[reveman, 2013-06-10 23:27:24]

lgtm

[commit-bot: I haz the power, 2013-06-10 23:33:03]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/boliu@chromium.org/16431003/4001

[commit-bot: I haz the power, 2013-06-11 03:56:21]

Retried try job too often on win7_aura for step(s) browser_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win7_aura&...

[commit-bot: I haz the power, 2013-06-11 03:57:31]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/boliu@chromium.org/16431003/4001

[commit-bot: I haz the power, 2013-06-11 12:40:40]

Change committed as 205510