cc: Only create tilings for layers that draws content.

cc: Only create tilings for layers that draws content.

BUG=164752
TEST=manual

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=171945

[reveman, 2012-12-07 16:39:18]

We currently waste time posting raster tasks with empty picture piles. Looks
like occlusion culling is the reason that's happening. This addresses that at
the tile manager level. It might be better to avoid creating tiles for these
layers in the first place.

[enne (OOO), 2012-12-07 17:37:29]

Yeah, I agree that it would be better to not create these tiles in the first
place.  I think you'd need just need to have PicturePileLayerImpl::CreateTile
return null if the pile is empty (and then handle that).  Optionally, you could
also skip creating any tilings for that layer.

[nduca, 2012-12-07 17:47:06]

Sorry, where are these tiles from?

[nduca, 2012-12-07 18:18:26]

Enne sorted me out offline. They can do the final review. Ima good.

[reveman, 2012-12-07 23:54:54]

This seems to be enough. There might still be occlusion culling cases but I'd
like to be able to reproduce that first.

[enne (OOO), 2012-12-08 00:03:18]

lgtm

[commit-bot: I haz the power, 2012-12-08 00:08:11]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/reveman@chromium.org/11467020/6001

[commit-bot: I haz the power, 2012-12-08 06:01:51]

Change committed as 171945