Move LayoutObject::m_previousPosition... into a global map in ObjectPaintInvalidator

third_party/WebKit/Source/core/paint/PaintInvalidator.cpp

Index: third_party/WebKit/Source/core/paint/PaintInvalidator.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintInvalidator.cpp b/third_party/WebKit/Source/core/paint/PaintInvalidator.cpp
index 18181096b12946f1b6250fee2c54a311780b5c3b..034de1800c61893e669e61be92efd5702badb36d 100644
--- a/third_party/WebKit/Source/core/paint/PaintInvalidator.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintInvalidator.cpp
@@ -151,9 +151,14 @@ LayoutRect PaintInvalidator::computeVisualRectInBacking(
   return mapLocalRectToPaintInvalidationBacking(object, localRect, context);
 }
 
-LayoutPoint PaintInvalidator::computeLocationFromPaintInvalidationBacking(
+LayoutPoint PaintInvalidator::computeLocationInBacking(
     const LayoutObject& object,
     const PaintInvalidatorContext& context) {
+  // Use visual rect location for LayoutTexts and non-container SVG objects
+  // because visual rect change suffices to detect layout caused invalidation.
+  if (!object.isBoxModelObject() && !object.isSVGContainer())

[chrishtr, 2016/11/04 18:20:07]

You say it suffices to use newVisualRect.location() for this objects. I presume
if you just let
the logic below execute, a lot more objects would get a value that is different
than
context.newVisualRect.location()?  How many?

[Xianzhu, 2016/11/04 19:11:03]

In the stat result from cluster telemetry:

Total number of LayoutObjects: 17,960,850
Objects that location != visualRect.location(): 3,255,651 {
  LayoutText: 2,438,061
  LayoutBox: 138,208
  LayoutInline: 427,867
  SVG: 264,137 (this may overlap with the above 3 making the total > 3,255,651)
}

LayoutText seems to use the location of its containing block, making almost all
LayoutTexts having location != visualRect.location().

I didn't measure the details of SVG. As the number is small, for simplicity we
can just check isText() here. Done.

+    return context.newVisualRect.location();
+
   FloatPoint point;
   if (object != context.paintInvalidationContainer) {
     point.moveBy(FloatPoint(context.treeBuilderContext.current.paintOffset));
@@ -322,11 +327,11 @@ void PaintInvalidator::updateContext(const LayoutObject& object,
     context.forcedSubtreeInvalidationFlags |=
         PaintInvalidatorContext::ForcedSubtreeSlowPathRect;
 
+  ObjectPaintInvalidator objectPaintInvalidator(object);
   context.oldVisualRect = object.previousVisualRect();
-  context.oldLocation = object.previousPositionFromPaintInvalidationBacking();
+  context.oldLocation = objectPaintInvalidator.previousLocationInBacking();
   context.newVisualRect = computeVisualRectInBacking(object, context);
-  context.newLocation =
-      computeLocationFromPaintInvalidationBacking(object, context);
+  context.newLocation = computeLocationInBacking(object, context);
 
   IntSize adjustment = object.scrollAdjustmentForPaintInvalidation(
       *context.paintInvalidationContainer);
@@ -334,8 +339,7 @@ void PaintInvalidator::updateContext(const LayoutObject& object,
   context.newVisualRect.move(adjustment);
 
   object.getMutableForPainting().setPreviousVisualRect(context.newVisualRect);
-  object.getMutableForPainting()
-      .setPreviousPositionFromPaintInvalidationBacking(context.newLocation);
+  objectPaintInvalidator.setPreviousLocationInBacking(context.newLocation);
 }
 
 void PaintInvalidator::invalidatePaintIfNeeded(