Remove const LayerImpl* from QuadSink

Remove const LayerImpl* from QuadSink

(Merged to previous CL 309493002)

QuadSink does not need keep track of LayerIml*. LayerImpl is only used
when calling Occluded[ContributingSurface]ContentRect function through
OcclusionTracker, and it only happens in AppendQuads function from
LayerImpl or RenderSurfaceImpl, where the needed LayerImpl can already
be found. In LayerImpl::AppendQuads, OcclusionTracker needs this, and
in RenderSurfaceImpl::AppendQuads, OT needs owning_layer_.

This CL is part of clean up QuadSink. Next CL should be able to remove
QuadSink and MockQuadCuller.

This CL follows 302603006, 306683002, and 309493002.

BUG=344962
TEST=cc_unittests

[enne (OOO), 2014-05-30 21:37:01]

lgtm

https://codereview.chromium.org/304203005/diff/1/cc/layers/quad_sink.cc
File cc/layers/quad_sink.cc (left):

https://codereview.chromium.org/304203005/diff/1/cc/layers/quad_sink.cc#oldco...
cc/layers/quad_sink.cc:23: layer_(layer),
Yay, much better.