Find cached display items directly during painting

third_party/WebKit/Source/platform/graphics/ContiguousContainer.cpp

Index: third_party/WebKit/Source/platform/graphics/ContiguousContainer.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/ContiguousContainer.cpp b/third_party/WebKit/Source/platform/graphics/ContiguousContainer.cpp
index cb42fefa480b0aa32f03d22131e9d8205945ed00..9da33c4b0d70b3130e0ebd3dba3bbe82d14a616b 100644
--- a/third_party/WebKit/Source/platform/graphics/ContiguousContainer.cpp
+++ b/third_party/WebKit/Source/platform/graphics/ContiguousContainer.cpp
@@ -171,6 +171,12 @@ void ContiguousContainerBase::swap(ContiguousContainerBase& other)
     std::swap(m_maxObjectSize, other.m_maxObjectSize);
 }
 
+void ContiguousContainerBase::removeEmptyBuffers()
+{
+    while (m_endIndex < m_buffers.size() - 1)

[jbroman, 2016/07/06 17:34:03]

How are we getting into a state where this is needed?
ContiguousContainerBase::removeLast should already be removing all but one empty
buffer.

[Xianzhu, 2016/07/06 18:05:27]

The method is to remove the last empty buffer. For a committed display item
list, because we will no more change the list, the empty buffer (which is big)
will be never used.

This was not needed because we copied the items in m_newDisplayItemList into
updatedList which doesn't have removeLast() calls so doesn't have the trailing
empty buffer, and then move updatedList into m_currentPaintArtifact. Now we move
m_newDisplayItemList into m_currentPaintArtifact directly. If there is any
trailing empty buffer it will be alive until the next paint.

[jbroman, 2016/07/06 19:09:37]

Ah, okay, it's a "shrink to fit"-ish thing. Makes sense.

+        m_buffers.removeLast();
+}
+
 ContiguousContainerBase::Buffer*
 ContiguousContainerBase::allocateNewBufferForNextAllocation(size_t bufferSize, const char* typeName)
 {