Reduce memory peaks when generating data urls for images.

Source/core/inspector/InspectorLayerTreeAgent.cpp

 /*
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 35 matching lines @@
 #include "core/rendering/compositing/CompositedLayerMapping.h"
 #include "core/rendering/compositing/RenderLayerCompositor.h"
 #include "platform/geometry/IntRect.h"
 #include "platform/graphics/CompositingReasons.h"
 #include "platform/graphics/GraphicsContextRecorder.h"
 #include "platform/image-encoders/skia/PNGImageEncoder.h"
 #include "platform/transforms/TransformationMatrix.h"
 #include "public/platform/WebFloatPoint.h"
 #include "public/platform/WebLayer.h"
 #include "wtf/text/Base64.h"
+#include "wtf/text/StringBuilder.h"
 
 namespace blink {
 
 unsigned InspectorLayerTreeAgent::s_lastSnapshotId;
 
 inline String idForLayer(const GraphicsLayer* graphicsLayer)
 {
     return String::number(graphicsLayer->platformLayer()->id());
 }
 
@@ skipping 310 matching lines @@
 void InspectorLayerTreeAgent::replaySnapshot(ErrorString* errorString, const String& snapshotId, const int* fromStep, const int* toStep, const double* scale, String* dataURL)
 {
     const GraphicsContextSnapshot* snapshot = snapshotById(errorString, snapshotId);
     if (!snapshot)
         return;
     OwnPtr<Vector<char> > base64Data = snapshot->replay(fromStep ? *fromStep : 0, toStep ? *toStep : 0, scale ? *scale : 1.0);
     if (!base64Data) {
         *errorString = "Image encoding failed";
         return;
     }
-    *dataURL = "data:image/png;base64," + *base64Data;
+    StringBuilder url;
+    url.appendLiteral("data:image/png;base64,");
+    url.reserveCapacity(url.length() + base64Data->size());
+    url.append(base64Data->begin(), base64Data->size());
+    *dataURL = url.toString();
 }
 
 void InspectorLayerTreeAgent::profileSnapshot(ErrorString* errorString, const String& snapshotId, const int* minRepeatCount, const double* minDuration, RefPtr<TypeBuilder::Array<TypeBuilder::Array<double> > >& outTimings)
 {
     const GraphicsContextSnapshot* snapshot = snapshotById(errorString, snapshotId);
     if (!snapshot)
         return;
     OwnPtr<GraphicsContextSnapshot::Timings> timings = snapshot->profile(minRepeatCount ? *minRepeatCount : 1, minDuration ? *minDuration : 0);
     outTimings = TypeBuilder::Array<TypeBuilder::Array<double> >::create();
     for (size_t i = 0; i < timings->size(); ++i) {
@@ skipping 21 matching lines @@
 void InspectorLayerTreeAgent::didRemovePageOverlay(const GraphicsLayer* layer)
 {
     size_t index = m_pageOverlayLayerIds.find(layer->platformLayer()->id());
     if (index == WTF::kNotFound)
         return;
     m_pageOverlayLayerIds.remove(index);
 }
 
 
 } // namespace blink