Don't compute viewport intersection if parent frame is throttled

If a RemoteFrameView is inside a throttled LocalFrameView with out-of-
date layout, then it's not possible to compute its viewport
intersection. In that case, just propagate an empty intersection (which
is probably correct, because a throttled frame is presumably off
screen).

BUG=711468
R=kenrb@chromium.org

Change-Id: Ie400c407871aab74561b4e34eefece17aa8c3e27
Reviewed-on: https://chromium-review.googlesource.com/1173345Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Commit-Queue: Stefan Zager <szager@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583002}

third_party/WebKit/LayoutTests/FlagExpectations/site-per-process

@@ -119,7 +119,6 @@ crbug.com/801992 http/tests/misc/iframe-script-modify-attr.html [ Pass Crash ]
 
 crbug.com/711468 virtual/gpu/fast/canvas/canvas-composite-image.html [ Pass Timeout ]
 crbug.com/711468 virtual/gpu/fast/canvas/canvas-scale-strokePath-shadow.html [ Pass Timeout ]
-crbug.com/711468 http/tests/intersection-observer/cross-origin-iframe-with-nesting.html [ Failure ]
 
 crbug.com/807675 http/tests/images/image-decode-in-frame.html [ Crash Failure ]
 

third_party/blink/renderer/core/frame/remote_frame_view.cc

@@ -64,7 +64,8 @@ RemoteFrameView* RemoteFrameView::Create(RemoteFrame* remote_frame) {
 }
 
 void RemoteFrameView::UpdateViewportIntersectionsForSubtree() {
-  if (!remote_frame_->OwnerLayoutObject())
+  LayoutEmbeddedContent* owner = remote_frame_->OwnerLayoutObject();
+  if (!owner)
     return;
 
   LocalFrameView* local_root_view =
@@ -72,17 +73,23 @@ void RemoteFrameView::UpdateViewportIntersectionsForSubtree() {
   if (!local_root_view)
     return;
 
+  IntRect viewport_intersection;
+  DocumentLifecycle::LifecycleState parent_state =
+      owner->GetDocument().Lifecycle().GetState();
+
+  // If the parent LocalFrameView is throttled and out-of-date, then we can't
+  // get any useful information.
+  if (parent_state >= DocumentLifecycle::kLayoutClean) {
     // Start with rect in remote frame's coordinate space. Then
-  // mapToVisualRectInAncestorSpace will move it to the local root's coordinate
-  // space and account for any clip from containing elements such as a
-  // scrollable div. Passing nullptr as an argument to
+    // mapToVisualRectInAncestorSpace will move it to the local root's
+    // coordinate space and account for any clip from containing elements such
+    // as a scrollable div. Passing nullptr as an argument to
     // mapToVisualRectInAncestorSpace causes it to be clipped to the viewport,
     // even if there are RemoteFrame ancestors in the frame tree.
     LayoutRect rect(0, 0, frame_rect_.Width(), frame_rect_.Height());
-  rect.Move(remote_frame_->OwnerLayoutObject()->ContentBoxOffset());
-  IntRect viewport_intersection;
-  if (remote_frame_->OwnerLayoutObject()->MapToVisualRectInAncestorSpace(
-          nullptr, rect, kUseGeometryMapper)) {
+    rect.Move(owner->ContentBoxOffset());
+    if (owner->MapToVisualRectInAncestorSpace(nullptr, rect,
+                                              kUseGeometryMapper)) {
       IntRect root_visible_rect(IntPoint(), local_root_view->Size());
       IntRect intersected_rect = EnclosingIntRect(rect);
       intersected_rect.Intersect(root_visible_rect);
@@ -91,19 +98,19 @@ void RemoteFrameView::UpdateViewportIntersectionsForSubtree() {
       // to the remote frame's coordinate space.
       FloatRect viewport_intersection_float =
           remote_frame_->OwnerLayoutObject()
-            ->AncestorToLocalQuad(local_root_view->GetLayoutView(),
-                                  FloatQuad(intersected_rect),
+              ->AncestorToLocalQuad(
+                  local_root_view->GetLayoutView(), FloatQuad(intersected_rect),
                   kTraverseDocumentBoundaries | kUseTransforms)
               .BoundingBox();
       viewport_intersection_float.Move(
           -remote_frame_->OwnerLayoutObject()->ContentBoxOffset());
       viewport_intersection = EnclosingIntRect(viewport_intersection_float);
     }
+  }
 
   if (viewport_intersection == last_viewport_intersection_)
     return;
 
-  // TODO(szager): Propagate occlusion information.
   last_viewport_intersection_ = viewport_intersection;
   remote_frame_->Client()->UpdateRemoteViewportIntersection(
       viewport_intersection);