Fix the bug that sticky element may not be correctly invalidated due to non-promotion

third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp

Index: third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
index 43d57ebe4b042d11783e96ac70281c34fc84ca55..0b1eb9b433b016759207fda0de01c27e897a68e2 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
@@ -272,9 +272,16 @@ void CompositingRequirementsUpdater::UpdateRecursive(
                                                 false) &
        kCompositingReasonOverflowScrollingTouch);
 
+  const bool moves_with_respect_to_compositing_ancestor =
+      layer->SticksToScroller();

[flackr, 2017/05/18 18:13:14]

Sorry, can you put both parts of the expression to this calculation here (and
move the comment up)? This moves with respect to compositing ancestor if it has
a non-root compositing ancestor and sticks to scroller.

[yigu, 2017/05/18 19:26:43]

Done.

   // TODO(chrishtr): use |hasCompositedScrollingAncestor| instead.
   const bool ignore_lcd_text =
-      current_recursion_data.has_composited_scrolling_ancestor_;
+      current_recursion_data.has_composited_scrolling_ancestor_ ||
+      // TODO(yigu): We should check if we have already lost lcd text. This
+      // would require tracking if we think the current compositing ancestor
+      // layer meets the requirements (i.e. opaque, integer transform, etc).

[flackr, 2017/05/18 18:13:14]

From your discussions with Chris, we also have to promote right now to work
around a bug of not being able to invalidate the ancestor after updating the
sticky layer position, right? (can you add this to the comment).

[yigu, 2017/05/18 19:26:43]

Done.

+      (moves_with_respect_to_compositing_ancestor &&
+       !current_recursion_data.compositing_ancestor_->IsRootLayer());
   direct_reasons |=
       compositing_reason_finder_.DirectReasons(layer, ignore_lcd_text);