Fix a crash when saving a <canvas> or <img> image which is large.

content/common/content_constants_internal.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/common/content_constants_internal.h"
 
 namespace content {
 
 const int kHungRendererDelayMs = 30000;
 
 const uint16 kMaxPluginSideLength = 1 << 15;
 // 8m pixels.
 const uint32 kMaxPluginSize = 8 << 20;
 
+// 10MiB
+const size_t kMaxLengthOfDataURLString = 1024 * 1024 * 10;
+
 const int kTraceEventBrowserProcessSortIndex = -6;
 const int kTraceEventRendererProcessSortIndex = -5;
 const int kTraceEventPluginProcessSortIndex = -4;
 const int kTraceEventPpapiProcessSortIndex = -3;
 const int kTraceEventPpapiBrokerProcessSortIndex = -2;
 const int kTraceEventGpuProcessSortIndex = -1;
 
 const int kTraceEventRendererMainThreadSortIndex = -1;
 
 } // namespace content