Don't bother checking for paint properties for classes that never need them.

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

Index: third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
index 42d0cb93ce21beee0ffb1afea870788548b22afd..4ae5bcc578987cb5f9f2e710b574e009ea44836c 100644
--- a/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp
@@ -1207,6 +1207,10 @@ void PaintPropertyTreeBuilder::UpdatePaintProperties(
   }
 }
 
+static inline bool MightNeedPaintProperties(const LayoutObject& object) {
+  return object.IsBoxModelObject() || object.IsSVG();

[pdr., 2017/05/15 21:32:45]

Why is IsSVG() needed?

[chrishtr, 2017/05/15 21:36:22]

NeedsSVGLocalToBorderBoxTransform, NeedsTransformForNonRootSVG and NeedsEffect
all
trigger on SVG roots or children.

+}
+
 void PaintPropertyTreeBuilder::UpdatePropertiesForSelf(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& full_context) {
@@ -1218,7 +1222,10 @@ void PaintPropertyTreeBuilder::UpdatePropertiesForSelf(
     context = PaintPropertyTreeBuilderFragmentContext();
   }
 
-  UpdatePaintProperties(object, full_context);
+  bool might_need_paint_properties = MightNeedPaintProperties(object);

[pdr., 2017/05/15 21:32:45]

It's important that this does not change between updates. In other words, a
layoutobject cannot change from not might-need-paint-properties to needing paint
properties. I think it would be useful if this variable and function reflected
that. Something like "ObjectTypeMightNeedPaintProperties"?

[chrishtr, 2017/05/15 21:36:22]

Indeed. Changed.

+
+  if (might_need_paint_properties)

[pdr., 2017/05/15 21:32:45]

Is the perf win just reducing the calls to this fn by one?

[chrishtr, 2017/05/15 21:36:22]

No. the perf win is not calling UpdatePaintProperties, which will
call a whole bunch of other functions, some of which call others
and have a bit of non-trivial logic, just to verify that text
nodes etc have no paint properties.

+    UpdatePaintProperties(object, full_context);
 
   bool is_actually_needed = false;
 #if DCHECK_IS_ON()
@@ -1236,7 +1243,7 @@ void PaintPropertyTreeBuilder::UpdatePropertiesForSelf(
       object, full_context.force_subtree_update);
 #endif
 
-  if (object.IsBoxModelObject() || object.IsSVG()) {
+  if (might_need_paint_properties) {
     UpdateTransform(object, context, full_context.force_subtree_update);
     UpdateCssClip(object, context, full_context.force_subtree_update);
     if (RuntimeEnabledFeatures::slimmingPaintV2Enabled()) {
@@ -1255,7 +1262,7 @@ void PaintPropertyTreeBuilder::UpdatePropertiesForSelf(
 void PaintPropertyTreeBuilder::UpdatePropertiesForChildren(
     const LayoutObject& object,
     PaintPropertyTreeBuilderContext& context) {
-  if (!object.IsBoxModelObject() && !object.IsSVG())
+  if (!MightNeedPaintProperties(object))
     return;
 
   for (auto& fragment_context : context.fragments) {