Revert 272635 "cc: Examine layers to determine if we're ready to..."

Revert 272635 "cc: Examine layers to determine if we're ready to..."

Caused layout test failures and out-of-memory errors on several Mac
bots on the Blink waterfall. See Issue 375206.

BUG=375206
> cc: Examine layers to determine if we're ready to activate.
> 
> This introduces a new mechanism for determining when
> we're ready to activate the pending tree. The tile
> priority is still used to determine when it's worth
> waking up the compositor thread and evaluating if
> we can activate. However, the actual check that
> determines if we're ready to activate doesn't rely
> on the state of scheduled raster tasks but is a
> synchronous call on each layer.
> 
> The result is a pending tree activation mechanism that
> is much easier to debug and validate for correctness,
> while still providing the performance benefits of the
> old mechanism by taking the "required to activate" field
> of the tile priority into account when scheduling tasks.
>  
> BUG=375206
> TEST=cc_unittests --gtest_filter=PictureLayerImplTest.AllTilesRequiredForActivationAreReadyToDraw
> 
> Review URL: https://codereview.chromium.org/287643004

TBR=reveman@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=272660

[Ken Russell (switch to Gerrit), 2014-05-24 00:52:40]

Committed patchset #1 manually as r272660 (tree was closed).