[Media Controls] Prevent ComputedStyleRef crash in overlay play button

This CL adds a check in MediaControlOverlayPlayButtonElement that
prevents a call to ComputedStyleRef is ComputedStyle is null. This
prevents a crash we're seeing in certain cases on Windows and Mac.

Bug: 870490
Change-Id: Ia45a7239084b267ce8a352fc0a825b5c992c5eea
Reviewed-on: https://chromium-review.googlesource.com/1173471Reviewed-by: Hayato Ito <hayato@chromium.org>
Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583523}

third_party/blink/renderer/core/dom/element.cc

@@ -3893,6 +3893,10 @@ void Element::StoreNonLayoutObjectComputedStyle(
   EnsureElementRareData().SetComputedStyle(std::move(style));
 }
 
+void Element::ClearComputedStyle() {
+  EnsureElementRareData().ClearComputedStyle();
+}
+
 AtomicString Element::ComputeInheritedLanguage() const {
   const Node* n = this;
   AtomicString value;

third_party/blink/renderer/core/dom/element.h

@@ -547,6 +547,8 @@ class CORE_EXPORT Element : public ContainerNode {
   bool ShouldStoreNonLayoutObjectComputedStyle(const ComputedStyle&) const;
   void StoreNonLayoutObjectComputedStyle(scoped_refptr<ComputedStyle>);
 
+  void ClearComputedStyle();
+
   // Methods for indicating the style is affected by dynamic updates (e.g.,
   // children changing, our position changing in our sibling list, etc.)
   bool StyleAffectedByEmpty() const {

third_party/blink/renderer/modules/media_controls/elements/media_control_overlay_play_button_element.cc

@@ -300,6 +300,11 @@ bool MediaControlOverlayPlayButtonElement::IsMouseEventOnInternalButton(
   if (!mouse_event.HasPosition())
     return true;
 
+  // TODO(https://crbug.com/873839): In what cases do we hit this?
+  // If the internal button or computed style are unavailable, default to yes.
+  if (!internal_button_ || !GetComputedStyle())
+    return true;
+
   // Find the zoom-adjusted internal button bounding box.
   DOMRect* box = internal_button_->getBoundingClientRect();
   float zoom = ComputedStyleRef().EffectiveZoom() /

third_party/blink/renderer/modules/media_controls/elements/media_control_overlay_play_button_element_test.cc

@@ -8,15 +8,30 @@
 #include "third_party/blink/renderer/core/css/css_property_value_set.h"
 #include "third_party/blink/renderer/core/dom/events/event.h"
 #include "third_party/blink/renderer/core/event_type_names.h"
+#include "third_party/blink/renderer/core/events/mouse_event.h"
+#include "third_party/blink/renderer/core/html/media/html_video_element.h"
 #include "third_party/blink/renderer/core/testing/page_test_base.h"
+#include "third_party/blink/renderer/modules/media_controls/media_controls_impl.h"
 
 namespace blink {
 
 class MediaControlOverlayPlayButtonElementTest : public PageTestBase {
  public:
   void SetUp() final {
-    // Create page and instance of AnimatedArrow to run tests on.
+    // Create page with video element with controls.
     PageTestBase::SetUp();
+    HTMLVideoElement* media_element = HTMLVideoElement::Create(GetDocument());
+    media_element->SetBooleanAttribute(HTMLNames::controlsAttr, true);
+    GetDocument().body()->AppendChild(media_element);
+
+    // Create instance of MediaControlOverlayPlayButtonElement for tests.
+    MediaControlsImpl* media_controls =
+        static_cast<MediaControlsImpl*>(media_element->GetMediaControls());
+    ASSERT_NE(nullptr, media_controls);
+    overlay_play_button_ =
+        new MediaControlOverlayPlayButtonElement(*media_controls);
+
+    // Create instance of AnimatedArrow to run tests on.
     arrow_element_ = new MediaControlOverlayPlayButtonElement::AnimatedArrow(
         "test", GetDocument());
     GetDocument().body()->AppendChild(arrow_element_);
@@ -42,6 +57,22 @@ class MediaControlOverlayPlayButtonElementTest : public PageTestBase {
     GetElementById("arrow-3")->DispatchEvent(*event);
   }
 
+  void RemoveInternalButton() {
+    overlay_play_button_->internal_button_ = nullptr;
+  }
+
+  void RemoveComputedStyle() { overlay_play_button_->ClearComputedStyle(); }
+
+  void TestKeepEventInNode() {
+    MouseEventInit mouse_initializer;
+    mouse_initializer.setView(GetDocument().domWindow());
+    mouse_initializer.setButton(1);
+
+    MouseEvent* mouse_event =
+        MouseEvent::Create(nullptr, EventTypeNames::click, mouse_initializer);
+    overlay_play_button_->KeepEventInNode(*mouse_event);
+  }
+
  private:
   bool SVGElementHasDisplayValue() {
     return GetElementById("jump")->InlineStyle()->HasProperty(
@@ -54,6 +85,7 @@ class MediaControlOverlayPlayButtonElementTest : public PageTestBase {
     return GetDocument().body()->getElementById(id);
   }
 
+  Persistent<MediaControlOverlayPlayButtonElement> overlay_play_button_;
   Persistent<MediaControlOverlayPlayButtonElement::AnimatedArrow>
       arrow_element_;
 };
@@ -79,4 +111,16 @@ TEST_F(MediaControlOverlayPlayButtonElementTest, ShowIncrementsCounter) {
   ExpectPresentAndShown();
 }
 
+TEST_F(MediaControlOverlayPlayButtonElementTest,
+       KeepEventInNodeDoesntCrashWithoutInternalButton) {
+  RemoveInternalButton();
+  TestKeepEventInNode();
+}
+
+TEST_F(MediaControlOverlayPlayButtonElementTest,
+       KeepEventInNodeDoesntCrashWithoutComputedStyle) {
+  RemoveComputedStyle();
+  TestKeepEventInNode();
+}
+
 }  // namespace blink