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

content/common/content_constants_internal.h

Index: content/common/content_constants_internal.h
diff --git a/content/common/content_constants_internal.h b/content/common/content_constants_internal.h
index 55a2ade35334e7af923b1d9eaba86a99e239fb49..cb0e3366aadd69a6c559875c24ee95d4bd7e568e 100644
--- a/content/common/content_constants_internal.h
+++ b/content/common/content_constants_internal.h
@@ -19,6 +19,9 @@ extern const uint16 kMaxPluginSideLength;
 // plugin.
 extern const uint32 kMaxPluginSize;
 
+// The maximum length of string as data url.
+extern const size_t kMaxLengthOfDataURLString;
+
 // Constants used to organize content processes in about:tracing.
 CONTENT_EXPORT extern const int kTraceEventBrowserProcessSortIndex;
 CONTENT_EXPORT extern const int kTraceEventRendererProcessSortIndex;