Update layer-pre-rendering for Chrome flag

src/gpu/SkGpuDevice.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkGpuDevice.h"
 
 #include "effects/GrBicubicEffect.h"
@@ skipping 1924 matching lines @@
     }
 }
 
 SkSurface* SkGpuDevice::newSurface(const SkImageInfo& info) {
     return SkSurface::NewRenderTarget(fContext, info, fRenderTarget->numSamples());
 }
 
 void SkGpuDevice::EXPERIMENTAL_optimize(SkPicture* picture) {
     SkPicture::AccelData::Key key = GPUAccelData::ComputeAccelDataKey();
 
+    const SkPicture::AccelData* existing = picture->EXPERIMENTAL_getAccelData(key);
+    if (NULL != existing) {
+        return;
+    }
+
     SkAutoTUnref<GPUAccelData> data(SkNEW_ARGS(GPUAccelData, (key)));
 
     picture->EXPERIMENTAL_addAccelData(data);
 
     GatherGPUInfo(picture, data);
 }
 
 static void wrap_texture(GrTexture* texture, int width, int height, SkBitmap* result) {
     SkImageInfo info = SkImageInfo::MakeN32Premul(width, height);
     result->setConfig(info);
     result->setPixelRef(SkNEW_ARGS(SkGrPixelRef, (info, texture)))->unref();
 }
 
 void SkGpuDevice::EXPERIMENTAL_purge(SkPicture* picture) {
 
 }
 
 bool SkGpuDevice::EXPERIMENTAL_drawPicture(SkCanvas* canvas, SkPicture* picture) {
 
     SkPicture::AccelData::Key key = GPUAccelData::ComputeAccelDataKey();
 
     const SkPicture::AccelData* data = picture->EXPERIMENTAL_getAccelData(key);
     if (NULL == data) {
         return false;
     }
 
     const GPUAccelData *gpuData = static_cast<const GPUAccelData*>(data);
 
+    if (0 == gpuData->numSaveLayers()) {
+        return false;
+    }
+
     SkAutoTArray<bool> pullForward(gpuData->numSaveLayers());
     for (int i = 0; i < gpuData->numSaveLayers(); ++i) {
         pullForward[i] = false;
     }
 
     SkRect clipBounds;
     if (!canvas->getClipBounds(&clipBounds)) {
         return true;
     }
     SkIRect query;
@@ skipping 137 matching lines @@
         GrCachedLayer* layer = fContext->getLayerCache()->findLayerOrCreate(picture, i);
 
         if (NULL != layer->getTexture()) {
             fContext->unlockScratchTexture(layer->getTexture());
             layer->setTexture(NULL);
         }
     }
 
     return true;
 }