Reduce memory peaks when generating data urls for images.

Source/platform/graphics/ImageBuffer.cpp

 /*
  * Copyright (c) 2008, Google Inc. All rights reserved.
  * Copyright (C) 2009 Dirk Schulze <krit@webkit.org>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. 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
@@ skipping 395 matching lines @@
             return false;
     } else {
         if (!PNGImageEncoder::encode(source, encodedImage))
             return false;
         ASSERT(mimeType == "image/png");
     }
 
     return true;
 }
 
+static String EncodedImageToDataURL(const Vector<char>& encodedImage, const String& mimeType)
+{
+    String base64Data = base64Encode(encodedImage);
+    return "data:" + mimeType + ";base64," + base64Data;
+}
+
 String ImageBuffer::toDataURL(const String& mimeType, const double* quality) const
 {
     ASSERT(MIMETypeRegistry::isSupportedImageMIMETypeForEncoding(mimeType));
 
     Vector<char> encodedImage;
     if (!isSurfaceValid() || !encodeImage(m_surface->bitmap(), mimeType, quality, &encodedImage))
         return "data:,";
-    Vector<char> base64Data;
-    base64Encode(encodedImage, base64Data);
-
-    return "data:" + mimeType + ";base64," + base64Data;
+    return EncodedImageToDataURL(encodedImage, mimeType);

[Noel Gordon, 2014/09/11 01:03:23]

/curious would writing this as

   return "data:" + mimeType + ";base64," + base64Encode(encodedImage);

do what you want here (interpolate a Sting)?

[Daniel Bratell, 2014/09/11 11:22:31]

It would work the same. I put it in a separate method because it's done in two
different methods, and despite being a 1-2 liner it is actually a fair bit of
generated code (string constructions, destructions, copies, lots of
StringAppend<> objects and it is unnecessary to have that more than once.

 }
 
 String ImageDataToDataURL(const ImageDataBuffer& imageData, const String& mimeType, const double* quality)
 {
     ASSERT(MIMETypeRegistry::isSupportedImageMIMETypeForEncoding(mimeType));
 
     Vector<char> encodedImage;
     if (!encodeImage(imageData, mimeType, quality, &encodedImage))
         return "data:,";
-
-    Vector<char> base64Data;
-    base64Encode(encodedImage, base64Data);
-
-    return "data:" + mimeType + ";base64," + base64Data;
+    return EncodedImageToDataURL(encodedImage, mimeType);
 }
 
 } // namespace blink