Add Drawing Manager guards against re-entrant flushes

src/gpu/GrDrawingManager.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrDrawContext.h"
 #include "GrDrawingManager.h"
 #include "GrDrawTarget.h"
@@ skipping 46 matching lines @@
 }
 
 void GrDrawingManager::reset() {
     for (int i = 0; i < fDrawTargets.count(); ++i) {
         fDrawTargets[i]->reset();
     }
     fFlushState.reset();
 }
 
 void GrDrawingManager::flush() {
+    if (fFlushing) {
+        return;
+    }
+    fFlushing = true;
+
     SkDEBUGCODE(bool result =) 
                         SkTTopoSort<GrDrawTarget, GrDrawTarget::TopoSortTraits>(&fDrawTargets);
     SkASSERT(result);
 
 #if 0
     for (int i = 0; i < fDrawTargets.count(); ++i) {
         SkDEBUGCODE(fDrawTargets[i]->dump();)
     }
 #endif
 
@@ skipping 23 matching lines @@
         SkASSERT(fDrawTargets.count() == 1);
         // Clear out this flag so the topological sort's SkTTopoSort_CheckAllUnmarked check
         // won't bark
         fDrawTargets[0]->resetFlag(GrDrawTarget::kWasOutput_Flag);
     }
 #else
     fDrawTargets.reset();
 #endif
 
     fFlushState.reset();
+    fFlushing = false;
 }
 
 GrTextContext* GrDrawingManager::textContext(const SkSurfaceProps& props,
                                              GrRenderTarget* rt) {
     if (this->abandoned()) {
         return nullptr;
     }
 
     SkASSERT(props.pixelGeometry() < kNumPixelGeometries);
     bool useDIF = props.isUseDeviceIndependentFonts();
@@ skipping 68 matching lines @@
 }
 
 GrDrawContext* GrDrawingManager::drawContext(GrRenderTarget* rt,
                                              const SkSurfaceProps* surfaceProps) {
     if (this->abandoned()) {
         return nullptr;
     }
 
     return new GrDrawContext(this, rt, surfaceProps);
 }