Enable blend optimizations with instanced draws

src/gpu/GrDrawTarget.cpp

Index: src/gpu/GrDrawTarget.cpp
diff --git a/src/gpu/GrDrawTarget.cpp b/src/gpu/GrDrawTarget.cpp
index fc3caf5212369b06a0de54fcd8d408df185b225f..86e0c82f225f1a6cf32e54602cb50c3c2375af82 100644
--- a/src/gpu/GrDrawTarget.cpp
+++ b/src/gpu/GrDrawTarget.cpp
@@ -33,6 +33,8 @@
 #include "batches/GrRectBatchFactory.h"
 #include "batches/GrStencilPathBatch.h"
 
+#include "instanced/InstancedRendering.h"
+
 ////////////////////////////////////////////////////////////////////////////////
 
 // Experimentally we have found that most batching occurs within the first 10 comparisons.
@@ -45,7 +47,8 @@ GrDrawTarget::GrDrawTarget(GrRenderTarget* rt, GrGpu* gpu, GrResourceProvider* r
     , fResourceProvider(resourceProvider)
     , fAuditTrail(auditTrail)
     , fFlags(0)
-    , fRenderTarget(rt) {
+    , fRenderTarget(rt)
+    , fInstancedRendering(fGpu->createInstancedRenderingIfSupported()) {
     // TODO: Stop extracting the context (currently needed by GrClipMaskManager)
     fContext = fGpu->getContext();
 
@@ -201,6 +204,10 @@ void GrDrawTarget::prepareBatches(GrBatchFlushState* flushState) {
             fBatches[i]->prepare(flushState);
         }
     }
+
+    if (fInstancedRendering) {
+        fInstancedRendering->beginFlush(flushState->resourceProvider());
+    }
 }
 
 void GrDrawTarget::drawBatches(GrBatchFlushState* flushState) {
@@ -269,6 +276,9 @@ void GrDrawTarget::drawBatches(GrBatchFlushState* flushState) {
 
 void GrDrawTarget::reset() {
     fBatches.reset();
+    if (fInstancedRendering) {
+        fInstancedRendering->endFlush();
+    }
 }
 
 void GrDrawTarget::drawBatch(const GrPipelineBuilder& pipelineBuilder,