Do not early out from the prepaint tree walk if a subtree walk is needed

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I36517164645aad4ac3132c8a510bb8ddab024a9f
Reviewed-on: https://chromium-review.googlesource.com/1086274
Commit-Queue: Philip Rogers <pdr@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#566425}

third_party/blink/renderer/core/paint/paint_invalidator.cc

@@ -596,7 +596,7 @@ void PaintInvalidator::InvalidatePaint(
   UpdatePaintInvalidationContainer(object, context);
   UpdateEmptyVisualRectFlag(object, context);
 
-  if (!object.ShouldCheckForPaintInvalidation() && !context.subtree_flags)
+  if (!object.ShouldCheckForPaintInvalidation() && !context.NeedsSubtreeWalk())
     return;
 
   unsigned tree_builder_index = 0;

third_party/blink/renderer/core/paint/paint_invalidator.h

@@ -54,6 +54,14 @@ struct CORE_EXPORT PaintInvalidatorContext {
            (subtree_flags & PaintInvalidatorContext::kSubtreeVisualRectUpdate);
   }
 
+  bool NeedsSubtreeWalk() const {
+    return subtree_flags &
+           (kSubtreeInvalidationChecking | kSubtreeVisualRectUpdate |
+            kSubtreeFullInvalidation |
+            kSubtreeFullInvalidationForStackedContents |
+            kSubtreeSVGResourceChange);
+  }
+
   const PaintInvalidatorContext* ParentContext() const {
     return parent_context_accessor_.ParentContext();
   }
@@ -64,6 +72,7 @@ struct CORE_EXPORT PaintInvalidatorContext {
   ParentContextAccessor parent_context_accessor_;
 
  public:
+  // When adding new subtree flags, ensure |NeedsSubtreeWalk| is updated.
   enum SubtreeFlag {
     kSubtreeInvalidationChecking = 1 << 0,
     kSubtreeVisualRectUpdate = 1 << 1,

third_party/blink/renderer/core/paint/pre_paint_tree_walk.cc

@@ -364,6 +364,7 @@ void PrePaintTreeWalk::Walk(const LayoutObject& object) {
   // Early out from the tree walk if possible.
   if (!needs_tree_builder_context_update &&
       !object.ShouldCheckForPaintInvalidation() &&
+      !parent_context().paint_invalidator_context.NeedsSubtreeWalk() &&
       !NeedsEffectiveWhitelistedTouchActionUpdate(object, parent_context()) &&
       !NeedsHitTestingPaintInvalidation(object, parent_context())) {
     return;