Simplified stencil buffer caching

This CL simplifies caching of stencil buffers by:
  removing the GrResourceCache::kSingle_LockType
  replacing GrStencilBuffer::fRTAttachmentCnt with nested locks from the reffing render targets

This CL also fixes a lock leak in the old system as can be observed in the 'Unlocked Entry Count' fields in the following.

BEFORE

config: gpu 4cad70
Budget: 256 items 16777216 bytes
                Entry Count: current 9 high 163
                Unlocked Entry Count: current 0 high 162
                Entry Bytes: current 11591600 high 198836800
                Detached Entry Count: current 0 high 13
                Detached Bytes: current 0 high 14133056

config: msaa16 12ad70
Budget: 256 items 16777216 bytes
                Entry Count: current 12 high 164
                Unlocked Entry Count: current 0 high 162
                Entry Bytes: current 217151232 high 317456128
                Detached Entry Count: current 0 high 13
                Detached Bytes: current 0 high 14133056

AFTER

config: gpu 6a2140
Budget: 256 items 16777216 bytes
                Entry Count: current 14 high 168
                Unlocked Entry Count: current 13 high 167
                Entry Bytes: current 9576980 high 198556800
                Detached Entry Count: current 0 high 13
                Detached Bytes: current 0 high 14133056

config: msaa16 802140
Budget: 256 items 16777216 bytes
                Entry Count: current 7 high 163
                Unlocked Entry Count: current 7 high 162
                Entry Bytes: current 14256000 high 216988800

[robertphillips, 2012-09-05 13:22:31]

http://codereview.appspot.com/6503073/diff/2001/src/gpu/GrGpu.cpp
File src/gpu/GrGpu.cpp (left):

http://codereview.appspot.com/6503073/diff/2001/src/gpu/GrGpu.cpp#oldcode159
src/gpu/GrGpu.cpp:159: rt->width(), rt->height())) {
These two lines were moved into createStencilBufferForRenderTarget. This is the
only use of that method.

[bsalomon, 2012-09-05 13:47:45]

LGTM (w/ 1 question)

http://codereview.appspot.com/6503073/diff/4001/src/gpu/gl/GrGLStencilBuffer.cpp
File src/gpu/gl/GrGLStencilBuffer.cpp (left):

http://codereview.appspot.com/6503073/diff/4001/src/gpu/gl/GrGLStencilBuffer....
src/gpu/gl/GrGLStencilBuffer.cpp:31: INHERITED::onRelease();
Did we have to remove these because they are pure virtual in the base class? I
wonder if that is wrong,

[robertphillips, 2012-09-05 15:47:13]

committed as r5400

https://codereview.appspot.com/6503073/diff/4001/src/gpu/gl/GrGLStencilBuffer...
File src/gpu/gl/GrGLStencilBuffer.cpp (left):

https://codereview.appspot.com/6503073/diff/4001/src/gpu/gl/GrGLStencilBuffer...
src/gpu/gl/GrGLStencilBuffer.cpp:31: INHERITED::onRelease();
That is why I had to remove them and I think it is wrong too. I will fix that
(and restore these) in a separate CL.