Check DisplayItemCient aliveness in cached subsequences

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

Index: third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp b/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
index f474b93a45cf01ec08a84531734f1bad0981aa85..1d8e59430e936ac72b4c6da089f9b55227d7aa7e 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintController.cpp
@@ -66,8 +66,26 @@ void PaintController::processNewItem(DisplayItem& displayItem)
     DCHECK(!skippingCache() || !displayItem.isCached());
 
 #if CHECK_DISPLAY_ITEM_CLIENT_ALIVENESS
-    if (!skippingCache() && (displayItem.isCacheable() || displayItem.isCached()))
-        displayItem.client().beginShouldKeepAlive(this);
+    if (!skippingCache()) {
+        if (displayItem.isCacheable() || displayItem.isCached()) {
+            // Mark the client shouldKeepAlive under this PaintController.
+            // The status will end after the new display items are committed.
+            displayItem.client().beginShouldKeepAlive(this);
+
+            if (!m_currentSubsequenceClients.isEmpty()) {
+                // Mark the client shouldKeepAlive under the current subsequence.
+                // The status will end when the subsequence owner is invalidated or deleted.
+                displayItem.client().beginShouldKeepAlive(m_currentSubsequenceClients.last());
+            }
+        }
+
+        if (displayItem.getType() == DisplayItem::Subsequence) {
+            m_currentSubsequenceClients.append(&displayItem.client());
+        } else if (displayItem.getType() == DisplayItem::EndSubsequence) {
+            CHECK(m_currentSubsequenceClients.last() == &displayItem.client());
+            m_currentSubsequenceClients.removeLast();
+        }
+    }
 #endif
 
     if (displayItem.isCached())
@@ -403,6 +421,7 @@ void PaintController::updateCacheGeneration()
         displayItem.client().setDisplayItemsCached(m_currentCacheGeneration);
     }
 #if CHECK_DISPLAY_ITEM_CLIENT_ALIVENESS
+    CHECK(m_currentSubsequenceClients.isEmpty());
     DisplayItemClient::endShouldKeepAliveAllClients(this);
 #endif
 }