Enable gpu Debug markers if tracing category skia.gpu is enabled

Enable gpu Debug markers if tracing category skia.gpu is enabled

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/6d7f5faeb3f1745bd1fb90c8a2a0655a9e416e4a

[bsalomon, 2014-08-04 15:22:06]

https://codereview.chromium.org/438023004/diff/1/src/gpu/GrContext.cpp
File src/gpu/GrContext.cpp (right):

https://codereview.chromium.org/438023004/diff/1/src/gpu/GrContext.cpp#newcod...
src/gpu/GrContext.cpp:114: // Check if the gpu.serivce category is set from
tracing and enable GpuTracing if it is
Is it really right to do this only when the GrContext is created? In practice I
think that has usually already occurred before tracing is invoked.

[egdaniel, 2014-08-04 19:04:24]

New version connects the enableGpuTracing to the skia.gpu flag to decide whether
or not to emit the gpu debug markers (gpu.service will still be required to be
turned on in order for chrome to read the markers).

Removed the old fGpuTracingEnabled flag from GrContext since the checks can all
be done within the macro.

[bsalomon, 2014-08-04 19:07:34]

lgtm w/ comment about var name uniqueness.

https://codereview.chromium.org/438023004/diff/40001/src/gpu/GrTracing.h
File src/gpu/GrTracing.h (right):

https://codereview.chromium.org/438023004/diff/40001/src/gpu/GrTracing.h#newc...
src/gpu/GrTracing.h:90: bool gpuTracingEnabled;                                 
                     \
If we're adding var names we should either append a line number or scope this in
{} to avoid collisions.

[egdaniel, 2014-08-04 19:44:07]

The CQ bit was checked by egdaniel@google.com

[commit-bot: I haz the power, 2014-08-04 19:44:28]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/egdaniel@google.com/438023004/60001

[commit-bot: I haz the power, 2014-08-04 19:54:43]

Change committed as 6d7f5faeb3f1745bd1fb90c8a2a0655a9e416e4a