Add hooks for GL_EXT_debug_marker in gpu

src/gpu/GrDrawTarget.h

Index: src/gpu/GrDrawTarget.h
diff --git a/src/gpu/GrDrawTarget.h b/src/gpu/GrDrawTarget.h
index c5058699b5ef880c2e2277099f7dae8e1c948d3e..547058f552dd9da69d8df46f942a53091933871b 100644
--- a/src/gpu/GrDrawTarget.h
+++ b/src/gpu/GrDrawTarget.h
@@ -423,6 +423,21 @@ public:
                        GrRenderTarget* renderTarget = NULL) = 0;
 
     /**
+     * Function calls to place debug markers in command stream. Must be implemented in derived class
+     * InsertEventMarker places a single "sign post" type marker into command stream. The argument
+     * marker will be the name of the annotation that is added.
+     */
+    virtual void insertEventMarker(const char* marker) {};

[bsalomon, 2014/02/20 22:14:13]

= 0?

Or make the GrDT track the push count and assert it's always >= 0. (and call
onFoo virtuals).

+    /**
+     * The following two functions are used for marking groups of commands. Use pushGroupMarker
+     * to set the beginning of a command set, and popGroupMarker is be called at end of the command
+     * set. The argument marker is the name for the annotation that is added. The push and pops
+     * can be used hierarchically, but every push must have a match pop.
+     */
+    virtual void pushGroupMarker(const char* marker) {};
+    virtual void popGroupMarker() {};
+
+    /**
      * Copies a pixel rectangle from one surface to another. This call may finalize
      * reserved vertex/index data (as though a draw call was made). The src pixels
      * copied are specified by srcRect. They are copied to a rect of the same