Create PaintChunk and begin writing code to build paint chunks.

third_party/WebKit/Source/platform/graphics/paint/PaintChunker.cpp

Index: third_party/WebKit/Source/platform/graphics/paint/PaintChunker.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/paint/PaintChunker.cpp b/third_party/WebKit/Source/platform/graphics/paint/PaintChunker.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..526b21e9ad04fc174862383263d1a67d52d3ca3f
--- /dev/null
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintChunker.cpp
@@ -0,0 +1,40 @@
+// Copyright 2015 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 "config.h"
+#include "platform/graphics/paint/PaintChunker.h"
+
+namespace blink {
+
+PaintChunker::PaintChunker()
+{
+}
+
+PaintChunker::~PaintChunker()
+{
+}
+
+void PaintChunker::updateCurrentPaintProperties(const PaintProperties& properties)

[trchen, 2015/10/01 02:19:36]

I think we can improve this a little bit.
IMO we should have a m_currentProperties. Whenever a new display item is
emitted, we check if m_currentProperties is the same as the last chunk, if yes,
append to the last chunk, otherwise create a new chunk. It will probably perform
better with case like this:

<draw/><clip></clip><draw/>

So both drawing can share a chunk without being interrupted by a no-op clip.

[jbroman, 2015/10/01 18:04:20]

I'd have expected that case to be rare, because Blink does have logic to avoid
emitting clips where no content would be clipped:

https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

I'm a little worried that the complexity will hurt incrementDisplayItemIndex's
cost, but not too worried. So sure, done.

+{
+    if (m_newChunk.properties == properties)
+        return;
+
+    if (m_newChunk.beginIndex != m_newChunk.endIndex)
+        m_chunks.append(m_newChunk);
+
+    m_newChunk = PaintChunk(m_newChunk.endIndex, m_newChunk.endIndex, properties);
+}
+
+Vector<PaintChunk> PaintChunker::releasePaintChunks()
+{
+    if (m_newChunk.beginIndex != m_newChunk.endIndex)
+        m_chunks.append(m_newChunk);
+
+    Vector<PaintChunk> chunks;
+    chunks.swap(m_chunks);
+    m_newChunk = PaintChunk();
+    return chunks;
+}
+
+} // namespace blink