Support GL_SAMPLES queries in null contexts

tools/gpu/gl/debug/GrRenderBufferObj.h

Index: tools/gpu/gl/debug/GrRenderBufferObj.h
diff --git a/tools/gpu/gl/debug/GrRenderBufferObj.h b/tools/gpu/gl/debug/GrRenderBufferObj.h
index 8231ef58dfba3c9c5bd6e8f2cfaf2f5acde261cf..134b9ec76314966aefe329c006c167729ba9a02f 100644
--- a/tools/gpu/gl/debug/GrRenderBufferObj.h
+++ b/tools/gpu/gl/debug/GrRenderBufferObj.h
@@ -30,6 +30,11 @@ public:
         this->INHERITED::deleteAction();
     }
 
+    void setNumSamples(int numSamples) {
+        GrAlwaysAssert(numSamples > 0);
+        fNumSamples = numSamples;
+    }
+
 protected:
 private:
     bool fBound;           // is this render buffer currently bound via "glBindRenderbuffer"?