Don't cache subsequence whose layer is not fully contained by repaint rect

Source/platform/graphics/paint/SubsequenceRecorder.cpp

Index: Source/platform/graphics/paint/SubsequenceRecorder.cpp
diff --git a/Source/platform/graphics/paint/SubsequenceRecorder.cpp b/Source/platform/graphics/paint/SubsequenceRecorder.cpp
index 4f54dbff0cc2797c37d6c7e5174a82f4f75ef98c..a45358459d5162723b5c56142e90ff2da14d2edf 100644
--- a/Source/platform/graphics/paint/SubsequenceRecorder.cpp
+++ b/Source/platform/graphics/paint/SubsequenceRecorder.cpp
@@ -33,11 +33,13 @@ bool SubsequenceRecorder::useCachedSubsequenceIfPossible(GraphicsContext& contex
 SubsequenceRecorder::SubsequenceRecorder(GraphicsContext& context, const DisplayItemClientWrapper& client)
     : m_displayItemList(context.displayItemList())
     , m_client(client)
+    , m_beginSubsequenceIndex(0)
 {
     if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled())
         return;
 
     ASSERT(m_displayItemList);
+    m_beginSubsequenceIndex = m_displayItemList->newDisplayItems().size();

[chrishtr, 2015/09/08 22:48:00]

You only need access to the size, not the whole vector. Just allowing access to
the former will be safer for the future.

[Xianzhu, 2015/09/09 16:50:33]

It's also needed to set uncacheable flag or a previous begin subsequence display
item (line 63 below).

     m_displayItemList->createAndAppend<BeginSubsequenceDisplayItem>(m_client);
 }
 
@@ -46,9 +48,19 @@ SubsequenceRecorder::~SubsequenceRecorder()
     if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled())
         return;
 
-    // Don't remove no-op BeginSubsequence/EndSubsequence pairs because we need to
-    // match them later with CachedSubsequences.
-    m_displayItemList->createAndAppend<EndSubsequenceDisplayItem>(m_client);
+    if (m_displayItemList->lastDisplayItemIsNoopBegin())
+        m_displayItemList->removeLastDisplayItem();
+    else
+        m_displayItemList->createAndAppend<EndSubsequenceDisplayItem>(m_client);
+}
+
+void SubsequenceRecorder::setUncacheable()
+{
+    if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled())
+        return;
+
+    ASSERT(m_displayItemList->newDisplayItems()[m_beginSubsequenceIndex].type() == DisplayItem::BeginSubsequence);
+    m_displayItemList->newDisplayItems()[m_beginSubsequenceIndex].setUncacheable();
 }
 
 } // namespace blink