Add hooks for GL_EXT_debug_marker in gpu

src/gpu/GrDrawTargetCaps.h

Index: src/gpu/GrDrawTargetCaps.h
diff --git a/src/gpu/GrDrawTargetCaps.h b/src/gpu/GrDrawTargetCaps.h
index b316e491c196ed4b8967099fdd2a4db2625cd51c..3e9081943057f36b67e60909ce085f755d30a164 100644
--- a/src/gpu/GrDrawTargetCaps.h
+++ b/src/gpu/GrDrawTargetCaps.h
@@ -40,6 +40,7 @@ public:
     bool bufferLockSupport() const { return fBufferLockSupport; }
     bool pathRenderingSupport() const { return fPathRenderingSupport; }
     bool dstReadInShaderSupport() const { return fDstReadInShaderSupport; }
+    bool debugMarkerSupport() const { return fDebugMarkerSupport; }
 
     // 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 @@ protected:
     bool fPathRenderingSupport      : 1;
     bool fDstReadInShaderSupport    : 1;
     bool fReuseScratchTextures      : 1;
+    bool fDebugMarkerSupport        : 1;
 
     int fMaxRenderTargetSize;
     int fMaxTextureSize;