Add hooks for GL_EXT_debug_marker in gpu

BUG=skia:
R=bsalomon@google.com

Author: egdaniel@google.com

Review URL: https://codereview.chromium.org/174123003

git-svn-id: http://skia.googlecode.com/svn/trunk@13538 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/gpu/GrDrawTargetCaps.h b/src/gpu/GrDrawTargetCaps.h
index b316e49..b33217a 100644
--- a/src/gpu/GrDrawTargetCaps.h
+++ b/src/gpu/GrDrawTargetCaps.h
@@ -40,6 +40,7 @@
     bool bufferLockSupport() const { return fBufferLockSupport; }
     bool pathRenderingSupport() const { return fPathRenderingSupport; }
     bool dstReadInShaderSupport() const { return fDstReadInShaderSupport; }
+    bool gpuTracingSupport() const { return fGpuTracingSupport; }
 
     // Scratch textures not being reused means that those scratch textures
     // that we upload to (i.e., don't have a render target) will not be
@@ -71,6 +72,7 @@
     bool fPathRenderingSupport      : 1;
     bool fDstReadInShaderSupport    : 1;
     bool fReuseScratchTextures      : 1;
+    bool fGpuTracingSupport         : 1;
 
     int fMaxRenderTargetSize;
     int fMaxTextureSize;