Register clipboard image blob in the browser process to copy data less.

third_party/WebKit/Source/core/clipboard/DataObjectItem.cpp

 /*
  * Copyright (C) 2011 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.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 98 matching lines @@
             return m_file.get();
         ASSERT(m_sharedBuffer);
         // FIXME: This code is currently impossible--we never populate m_sharedBuffer when dragging
         // in. At some point though, we may need to support correctly converting a shared buffer
         // into a file.
         return nullptr;
     }
 
     ASSERT(m_source == PasteboardSource);
     if (type() == mimeTypeImagePng) {
-        // FIXME: This is pretty inefficient. We copy the data from the browser
-        // to the renderer. We then place it in a blob in WebKit, which
-        // registers it and copies it *back* to the browser. When a consumer
-        // wants to read the data, we then copy the data back into the renderer.
-        // https://bugs.webkit.org/show_bug.cgi?id=58107 has been filed to track
-        // improvements to this code (in particular, add a registerClipboardBlob
-        // method to the blob registry; that way the data is only copied over
-        // into the renderer when it's actually read, not when the blob is
-        // initially constructed).
-        RefPtr<SharedBuffer> data = static_cast<PassRefPtr<SharedBuffer>>(Platform::current()->clipboard()->readImage(WebClipboard::BufferStandard));
-        OwnPtr<BlobData> blobData = BlobData::create();
-        blobData->appendBytes(data->data(), data->size());
-        blobData->setContentType(mimeTypeImagePng);
-        return Blob::create(BlobDataHandle::create(blobData.release(), data->size()));
+        WebBlobInfo blobInfo = Platform::current()->clipboard()->readImage(WebClipboard::BufferStandard);
+        if (blobInfo.size() < 0)
+            return nullptr;
+        return Blob::create(BlobDataHandle::create(blobInfo.uuid(), blobInfo.type(), blobInfo.size()));

[dmurph, 2016/04/12 00:10:23]

Hmmm.. Well if you went the register-blob-in-dispatcher-host-before-sending-it
approach, you would just call 
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

right after creating the blob here. Doing it this (hacky) way would require
documentation on the browser saying "please decrement the refcount once from the
renderer once you create the handle there".

maybe that's not the best way though haha

     }
 
     return nullptr;
 }
 
 String DataObjectItem::getAsString() const
 {
     ASSERT(m_kind == StringKind);
 
     if (m_source == InternalSource)
@@ skipping 23 matching lines @@
     // we'll need to make sure this works as expected for DragDataChromium.
     return m_kind == FileKind && m_file;
 }
 
 DEFINE_TRACE(DataObjectItem)
 {
     visitor->trace(m_file);
 }
 
 } // namespace blink