[LayoutNG] Trace block flow invalidation for devtools

This patch allows block-level NGPaintFragment invalidations to be
traced, to make relevant layout tests pass.

Note: This is a hacky fix only for making tests pass, since devtools
invalidation tracking is still an experimental feature. More work will
be done if the feature is launched.

Bug: 880519
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng;luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I6bfcd0204a66ea266e2de7a6a421fea29dc70fbf
Reviewed-on: https://chromium-review.googlesource.com/1204851Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589101}

third_party/WebKit/LayoutTests/FlagExpectations/enable-blink-features=LayoutNG

@@ -439,11 +439,6 @@ crbug.com/591099 http/tests/devtools/elements/shadow/shadow-distribution.js [ Fa
 crbug.com/591099 http/tests/devtools/network/network-datareceived.js [ Failure ]
 crbug.com/591099 http/tests/devtools/network/network-datasaver-warning.js [ Failure ]
 crbug.com/591099 http/tests/devtools/persistence/persistence-merge-editor-tabs.js [ Failure ]
-crbug.com/591099 http/tests/devtools/tracing/timeline-misc/timeline-grouped-invalidations.js [ Failure ]
-crbug.com/591099 http/tests/devtools/tracing/timeline-paint/timeline-paint-and-multiple-style-invalidations.js [ Failure ]
-crbug.com/591099 http/tests/devtools/tracing/timeline-paint/timeline-paint-with-layout-invalidations-on-deleted-node.js [ Timeout ]
-crbug.com/591099 http/tests/devtools/tracing/timeline-paint/timeline-paint-with-layout-invalidations.js [ Failure ]
-crbug.com/591099 http/tests/devtools/tracing/timeline-paint/timeline-paint-with-style-recalc-invalidations.js [ Failure ]
 crbug.com/591099 http/tests/images/restyle-decode-error.html [ Failure ]
 crbug.com/591099 http/tests/local/fileapi/select-dragged-file-input.html [ Skip ]
 crbug.com/591099 http/tests/misc/object-embedding-svg-delayed-size-negotiation.xhtml [ Failure ]

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

@@ -171,6 +171,19 @@ void ObjectPaintInvalidator::
   traverse(object_);
 }
 
+namespace {
+bool IsClientNGPaintFragmentForObject(const DisplayItemClient& client,
+                                      const LayoutObject& object) {
+  if (!RuntimeEnabledFeatures::LayoutNGEnabled())
+    return false;
+  // TODO(crbug.com/880519): This hack only makes current invalidation tracking
+  // layout tests pass with LayoutNG. More work is needed if we want to launch
+  // the invalidation tracking feature.
+  return object.IsLayoutBlockFlow() &&
+         &client == ToLayoutBlockFlow(object).PaintFragment();
+}
+}  // namespace
+
 void ObjectPaintInvalidator::InvalidateDisplayItemClient(
     const DisplayItemClient& client,
     PaintInvalidationReason reason) {
@@ -180,7 +193,8 @@ void ObjectPaintInvalidator::InvalidateDisplayItemClient(
   // reduce the cost.
   DCHECK(!object_.PaintingLayer() || object_.PaintingLayer()->NeedsRepaint());
 
-  if (&client == &object_) {
+  if (&client == &object_ ||
+      IsClientNGPaintFragmentForObject(client, object_)) {
     TRACE_EVENT_INSTANT1(
         TRACE_DISABLED_BY_DEFAULT("devtools.timeline.invalidationTracking"),
         "PaintInvalidationTracking", TRACE_EVENT_SCOPE_THREAD, "data",