New PaintController under-invalidation checking

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

Index: third_party/WebKit/Source/platform/graphics/paint/PaintController.h
diff --git a/third_party/WebKit/Source/platform/graphics/paint/PaintController.h b/third_party/WebKit/Source/platform/graphics/paint/PaintController.h
index 28324670645b376f8e760f71a4ddbeda6c121aeb..be361ce4511ce4085dac1290e1e2cdfef1233ba1 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PaintController.h
+++ b/third_party/WebKit/Source/platform/graphics/paint/PaintController.h
@@ -212,8 +212,9 @@ private:
 #if DCHECK_IS_ON()
     // The following two methods are for checking under-invalidations
     // (when RuntimeEnabledFeatures::slimmingPaintUnderInvalidationCheckingEnabled).
-    void checkUnderInvalidation(DisplayItemList::iterator& newIt, DisplayItemList::iterator& currentIt);
-    void checkCachedDisplayItemIsUnchanged(const char* messagePrefix, const DisplayItem& newItem, const DisplayItem& oldItem);
+    void showUnderInvalidationError(const char* reason, const DisplayItem& newItem, const DisplayItem& oldItem) const;
+    void checkUnderInvalidation();
+    bool isCheckingUnderInvalidation() const { return m_underInvalidationCheckingEnd - m_underInvalidationCheckingBegin > 0; }
 #endif
 
     // The last complete paint artifact.
@@ -262,6 +263,15 @@ private:
 
     // This is used to check duplicated ids during createAndAppend().
     DisplayItemIndicesByClientMap m_newDisplayItemIndicesByClient;
+
+    // These are set in useCachedDrawingIfPossible() and useCachedSubsequenceIfPossible()
+    // when we could use cached drawing or subsequence and under-invalidation checking is on,
+    // indicating the begin and end of the cached drawing or subsequence in the current list.
+    // The functions return false to let the client do actual painting, and PaintController
+    // will check if the actual painting results are the same as the cached.
+    DisplayItemList::iterator m_underInvalidationCheckingBegin;
+    DisplayItemList::iterator m_underInvalidationCheckingEnd;
+    String m_underInvalidationMessagePrefix;
 #endif
 
 #if CHECK_DISPLAY_ITEM_CLIENT_ALIVENESS