Enable subsequence caching for spv2

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

Index: third_party/WebKit/Source/platform/graphics/paint/PaintArtifact.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/paint/PaintArtifact.cpp b/third_party/WebKit/Source/platform/graphics/paint/PaintArtifact.cpp
index c61fd4d4840e1eb20215fe848aed6dd1eea044b4..5247ddb266c3adfd8fafac494416ff16876587a8 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PaintArtifact.cpp
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintArtifact.cpp
@@ -77,6 +77,20 @@ PaintArtifact& PaintArtifact::operator=(PaintArtifact&& source)
     return *this;
 }
 
+static bool compareChunkAndIndex(const PaintChunk& chunk, unsigned index)

[pdr., 2016/07/26 16:54:21]

Should all of these unsigned be size_t (here, and in PaintChunk)?

[Xianzhu, 2016/07/26 17:01:43]

Do you know what was the reason that we chose unsigned in PaintChunk? One reason
I guess is to limit size of chunks on 64-bit systems. Wdyt?

+{
+    return chunk.endIndex <= index;
+}
+
+Vector<PaintChunk>::const_iterator PaintArtifact::findChunkByDisplayItemIndex(unsigned index) const
+{
+    auto chunkIt = std::lower_bound(m_paintChunks.begin(), m_paintChunks.end(), index, compareChunkAndIndex);
+    DCHECK(chunkIt != m_paintChunks.end());
+    DCHECK(index >= chunkIt->beginIndex);
+    DCHECK(index < chunkIt->endIndex);
+    return chunkIt;
+}
+
 void PaintArtifact::reset()
 {
     m_displayItemList.clear();