Modify gpu debug markers to store gpu device markers when a flush occurs.

src/gpu/GrTraceMarker.h

Index: src/gpu/GrTraceMarker.h
diff --git a/src/gpu/GrTraceMarker.h b/src/gpu/GrTraceMarker.h
index 7cc2f7f9552012b6e9db71ce9c3cb4737826d58e..fa4904e0c9c270aa21cb80f69c0b2d92ae6ff667 100644
--- a/src/gpu/GrTraceMarker.h
+++ b/src/gpu/GrTraceMarker.h
@@ -65,4 +65,34 @@ private:
     mutable SkTDArray<GrGpuTraceMarker> fMarkerArray;
 };
 
+class GrTraceMarkerSet::Iter {
+public:
+    Iter() {};
+    Iter& operator=(const Iter& i) {
+        fCurrentIndex = i.fCurrentIndex;
+        fMarkers = i.fMarkers;
+        return *this;
+    }
+    bool operator==(const Iter& i) const {
+        return fCurrentIndex == i.fCurrentIndex && fMarkers == i.fMarkers;
+    }
+    bool operator!=(const Iter& i) const { return !(*this == i); }
+    const GrGpuTraceMarker& operator*() const { return fMarkers->fMarkerArray[fCurrentIndex]; }
+    Iter& operator++() {
+        SkASSERT(*this != fMarkers->end());
+        ++fCurrentIndex;
+        return *this;
+    }
+
+private:
+    friend class GrTraceMarkerSet;
+    Iter(const GrTraceMarkerSet* markers, int index)
+            : fMarkers(markers), fCurrentIndex(index) {
+        SkASSERT(markers);
+    }
+
+    const GrTraceMarkerSet* fMarkers;
+    int fCurrentIndex;
+};
+
 #endif