Create PaintChunk and begin writing code to build paint chunks.

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

Index: third_party/WebKit/Source/platform/graphics/paint/PaintChunker.h
diff --git a/third_party/WebKit/Source/platform/graphics/paint/PaintChunker.h b/third_party/WebKit/Source/platform/graphics/paint/PaintChunker.h
new file mode 100644
index 0000000000000000000000000000000000000000..536f9691349b8c1b81a8d2eb1a029b15428449b9
--- /dev/null
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintChunker.h
@@ -0,0 +1,41 @@
+// 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.
+
+#ifndef PaintChunker_h
+#define PaintChunker_h
+
+#include "platform/PlatformExport.h"
+#include "platform/graphics/paint/PaintChunk.h"
+#include "platform/graphics/paint/PaintProperties.h"
+#include "wtf/Vector.h"
+
+namespace blink {
+
+// Accepts information about changes to |PaintProperties| as drawings are
+// accumulated, and produces a series of paint chunks: contiguous ranges of the
+// display list with identical |PaintProperties|.
+class PLATFORM_EXPORT PaintChunker {
+public:
+    PaintChunker();
+    ~PaintChunker();
+
+    bool isInInitialState() const { return m_chunks.isEmpty() && m_newChunk == PaintChunk(); }
+
+    void updateCurrentPaintProperties(const PaintProperties&);
+
+    void incrementDisplayItemIndex() { m_newChunk.endIndex++; }
+    void decrementDisplayItemIndex() { ASSERT(m_newChunk.endIndex > 0); m_newChunk.endIndex--; }
+
+    // Releases the generated paint chunk list and resets the state of this
+    // object.
+    Vector<PaintChunk> releasePaintChunks();
+
+private:
+    Vector<PaintChunk> m_chunks;
+    PaintChunk m_newChunk;

[pdr., 2015/10/01 00:32:48]

Is there a reason for not putting this as the last item in m_chunks? This
approach isn't bad, just curious if we could remove the need for an "initial
state" concept (and the empty PaintChunk ctor) in favor of explicitly tracking
it with a bool.

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

Changed to trchen's suggestion. (I did this because it seemed simplest.)

+};
+
+} // namespace blink
+
+#endif // PaintChunker_h