Re-land^2 WebVR compositor bypass via BrowserMain context + mailbox

third_party/WebKit/Source/modules/vr/VRDisplay.cpp

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "modules/vr/VRDisplay.h"
 
 #include "core/css/StylePropertySet.h"
 #include "core/dom/DOMException.h"
 #include "core/dom/DocumentUserGestureToken.h"
 #include "core/dom/FrameRequestCallback.h"
-#include "core/dom/Fullscreen.h"
 #include "core/dom/ScriptedAnimationController.h"
 #include "core/dom/TaskRunnerHelper.h"
+#include "core/frame/FrameView.h"
+#include "core/frame/ImageBitmap.h"
 #include "core/frame/UseCounter.h"
 #include "core/inspector/ConsoleMessage.h"
+#include "core/layout/LayoutView.h"
+#include "core/layout/compositing/PaintLayerCompositor.h"
 #include "core/loader/DocumentLoader.h"
 #include "gpu/command_buffer/client/gles2_interface.h"
+#include "gpu/command_buffer/common/mailbox_holder.h"
 #include "modules/EventTargetModules.h"
 #include "modules/vr/NavigatorVR.h"
 #include "modules/vr/VRController.h"
 #include "modules/vr/VRDisplayCapabilities.h"
 #include "modules/vr/VREyeParameters.h"
 #include "modules/vr/VRFrameData.h"
 #include "modules/vr/VRLayer.h"
 #include "modules/vr/VRPose.h"
 #include "modules/vr/VRStageParameters.h"
 #include "modules/webgl/WebGLRenderingContextBase.h"
 #include "platform/Histogram.h"
 #include "platform/UserGestureIndicator.h"
+#include "platform/instrumentation/tracing/TraceEvent.h"
 #include "public/platform/Platform.h"
 #include "wtf/AutoReset.h"
 #include "wtf/Time.h"
 
 #include <array>
 
 namespace blink {
 
 namespace {
 
-// Magic numbers used to mark valid pose index values encoded in frame
-// data. Must match the magic numbers used in vr_shell.cc.
-static constexpr std::array<uint8_t, 2> kWebVrPosePixelMagicNumbers{{42, 142}};
-
 VREye stringToVREye(const String& whichEye) {
   if (whichEye == "left")
     return VREyeLeft;
   if (whichEye == "right")
     return VREyeRight;
   return VREyeNone;
 }
 
 }  // namespace
 
 VRDisplay::VRDisplay(NavigatorVR* navigatorVR,
                      device::mojom::blink::VRDisplayPtr display,
                      device::mojom::blink::VRDisplayClientRequest request)
     : ContextLifecycleObserver(navigatorVR->document()),
       m_navigatorVR(navigatorVR),
       m_capabilities(new VRDisplayCapabilities()),
       m_eyeParametersLeft(new VREyeParameters()),
       m_eyeParametersRight(new VREyeParameters()),
-      m_fullscreenCheckTimer(
-          TaskRunnerHelper::get(TaskType::UnspecedTimer,
-                                navigatorVR->document()->frame()),
-          this,
-          &VRDisplay::onFullscreenCheck),
       m_display(std::move(display)),
+      m_submit_frame_client_binding(this),
       m_displayClientBinding(this, std::move(request)) {}
 
 VRDisplay::~VRDisplay() {}
 
 VRController* VRDisplay::controller() {
   return m_navigatorVR->controller();
 }
 
 void VRDisplay::update(const device::mojom::blink::VRDisplayInfoPtr& display) {
   m_displayId = display->index;
@@ skipping 154 matching lines @@
   // allowed outside a user gesture so that the presented content may be
   // updated.
   if (firstPresent && !UserGestureIndicator::utilizeUserGesture()) {
     DOMException* exception = DOMException::create(
         InvalidStateError, "API can only be initiated by a user gesture.");
     resolver->reject(exception);
     ReportPresentationResult(PresentationResult::NotInitiatedByUserGesture);
     return promise;
   }
 
-  // TODO(mthiesse): Remove fullscreen requirement for presentation. See
-  // crbug.com/687369
-  Document* doc = this->document();
-  if (!doc || !Fullscreen::fullscreenEnabled(*doc)) {
-    DOMException* exception =
-        DOMException::create(InvalidStateError, "Fullscreen is not enabled.");
-    resolver->reject(exception);
-    ReportPresentationResult(PresentationResult::FullscreenNotEnabled);
-    return promise;
-  }
-
   // A valid number of layers must be provided in order to present.
   if (layers.size() == 0 || layers.size() > m_capabilities->maxLayers()) {
     forceExitPresent();
     DOMException* exception =
         DOMException::create(InvalidStateError, "Invalid number of layers.");
     resolver->reject(exception);
     ReportPresentationResult(PresentationResult::InvalidNumberOfLayers);
     return promise;
   }
 
@@ skipping 54 matching lines @@
     bool secureContext = scriptState->getExecutionContext()->isSecureContext();
     if (!m_display) {
       forceExitPresent();
       DOMException* exception = DOMException::create(
           InvalidStateError, "The service is no longer active.");
       resolver->reject(exception);
       return promise;
     }
 
     m_pendingPresentResolvers.append(resolver);
-    m_display->RequestPresent(secureContext, convertToBaseCallback(WTF::bind(
-                                                 &VRDisplay::onPresentComplete,
-                                                 wrapPersistent(this))));
+    m_submit_frame_client_binding.Close();
+    m_display->RequestPresent(
+        secureContext,
+        m_submit_frame_client_binding.CreateInterfacePtrAndBind(),
+        convertToBaseCallback(
+            WTF::bind(&VRDisplay::onPresentComplete, wrapPersistent(this))));
   } else {
     updateLayerBounds();
     resolver->resolve();
     ReportPresentationResult(PresentationResult::SuccessAlreadyPresenting);
   }
 
   return promise;
 }
 
 void VRDisplay::onPresentComplete(bool success) {
@@ skipping 48 matching lines @@
         "VR Presentation not implemented for this VRDisplay.");
     while (!m_pendingPresentResolvers.isEmpty()) {
       ScriptPromiseResolver* resolver = m_pendingPresentResolvers.takeFirst();
       resolver->reject(exception);
     }
     ReportPresentationResult(
         PresentationResult::PresentationNotSupportedByDisplay);
     return;
   } else {
     if (m_layer.source().isHTMLCanvasElement()) {
-      HTMLCanvasElement* canvas = m_layer.source().getAsHTMLCanvasElement();
-      // TODO(klausw,crbug.com/655722): Need a proper VR compositor, but
-      // for the moment on mobile we'll just make the canvas fullscreen
-      // so that VrShell can pick it up through the standard (high
-      // latency) compositing path.      auto canvas =
-      // m_layer.source().getAsHTMLCanvasElement();
-      auto inlineStyle = canvas->inlineStyle();
-      if (inlineStyle) {
-        // THREE.js's VREffect sets explicit style.width/height on its rendering
-        // canvas based on the non-fullscreen window dimensions, and it keeps
-        // those unchanged when presenting. Unfortunately it appears that a
-        // fullscreened canvas just gets centered if it has explicitly set a
-        // size smaller than the fullscreen dimensions. Manually set size to
-        // 100% in this case and restore it when exiting fullscreen. This is a
-        // stopgap measure since THREE.js's usage appears legal according to the
-        // WebVR API spec. This will no longer be necessary once we can get rid
-        // of this fullscreen hack.
-        m_fullscreenOrigWidth = inlineStyle->getPropertyValue(CSSPropertyWidth);
-        if (!m_fullscreenOrigWidth.isNull()) {
-          canvas->setInlineStyleProperty(CSSPropertyWidth, "100%");
-        }
-        m_fullscreenOrigHeight =
-            inlineStyle->getPropertyValue(CSSPropertyHeight);
-        if (!m_fullscreenOrigHeight.isNull()) {
-          canvas->setInlineStyleProperty(CSSPropertyHeight, "100%");
-        }
-      } else {
-        m_fullscreenOrigWidth = String();
-        m_fullscreenOrigHeight = String();
-      }
-
-      if (doc) {
-        // Since the callback for requestPresent is asynchronous, we've lost our
-        // UserGestureToken, and need to create a new one to enter fullscreen.
-        gestureIndicator = WTF::wrapUnique(
-            new UserGestureIndicator(DocumentUserGestureToken::create(
-                doc, UserGestureToken::Status::PossiblyExistingGesture)));
-      }
-      Fullscreen::requestFullscreen(*canvas);
-
-      // Check to see if the canvas is still the current fullscreen
-      // element once every 2 seconds.
-      m_fullscreenCheckTimer.startRepeating(2.0, BLINK_FROM_HERE);
-      m_reenteredFullscreen = false;
+      // TODO(klausw,crbug.com/698923): suppress compositor updates
+      // since they aren't needed, they do a fair amount of extra
+      // work.
     } else {
       DCHECK(m_layer.source().isOffscreenCanvas());
       // TODO(junov, crbug.com/695497): Implement OffscreenCanvas presentation
       forceExitPresent();
       DOMException* exception = DOMException::create(
           InvalidStateError, "OffscreenCanvas presentation not implemented.");
       while (!m_pendingPresentResolvers.isEmpty()) {
         ScriptPromiseResolver* resolver = m_pendingPresentResolvers.takeFirst();
         resolver->reject(exception);
       }
@@ skipping 60 matching lines @@
   } else {
     // Right eye defaults
     rightBounds->left = 0.5f;
     rightBounds->top = 0.0f;
     rightBounds->width = 0.5f;
     rightBounds->height = 1.0f;
     m_layer.setRightBounds({0.5f, 0.0f, 0.5f, 1.0f});
   }
 
   m_display->UpdateLayerBounds(m_vrFrameId, std::move(leftBounds),
-                               std::move(rightBounds));
+                               std::move(rightBounds), m_sourceWidth,
+                               m_sourceHeight);
 }
 
 HeapVector<VRLayer> VRDisplay::getLayers() {
   HeapVector<VRLayer> layers;
 
   if (m_isPresenting) {
     layers.push_back(m_layer);
   }
 
   return layers;
 }
 
 void VRDisplay::submitFrame() {
   if (!m_display)
     return;
+  TRACE_EVENT1("gpu", "submitFrame", "frame", m_vrFrameId);
 
   Document* doc = this->document();
   if (!m_isPresenting) {
     if (doc) {
       doc->addConsoleMessage(ConsoleMessage::create(
           RenderingMessageSource, WarningMessageLevel,
           "submitFrame has no effect when the VRDisplay is not presenting."));
     }
     return;
   }
 
   if (!m_inAnimationFrame) {
     if (doc) {
       doc->addConsoleMessage(
           ConsoleMessage::create(RenderingMessageSource, WarningMessageLevel,
                                  "submitFrame must be called within a "
                                  "VRDisplay.requestAnimationFrame callback."));
     }
     return;
   }
 
   if (!m_contextGL) {
     // Something got confused, we can't submit frames without a GL context.
     return;
   }
 
   // No frame Id to write before submitting the frame.
   if (m_vrFrameId < 0) {
-    m_display->SubmitFrame(m_framePose.Clone());
+    // TODO(klausw): There used to be a submitFrame here, but we can't
+    // submit without a frameId and associated pose data. Just drop it.
     return;
   }
 
-  // Write the frame number for the pose used into a bottom left pixel block.
-  // It is read by chrome/browser/android/vr_shell/vr_shell.cc to associate
-  // the correct corresponding pose for submission.
-  auto gl = m_contextGL;
+  m_contextGL->Flush();
 
-  // We must ensure that the WebGL app's GL state is preserved. We do this by
-  // calling low-level GL commands directly so that the rendering context's
-  // saved parameters don't get overwritten.
+  // Check if the canvas got resized, if yes send a bounds update.
+  int currentWidth = m_renderingContext->drawingBufferWidth();
+  int currentHeight = m_renderingContext->drawingBufferHeight();
+  if ((currentWidth != m_sourceWidth || currentHeight != m_sourceHeight) &&
+      currentWidth != 0 && currentHeight != 0) {
+    m_sourceWidth = currentWidth;
+    m_sourceHeight = currentHeight;
+    updateLayerBounds();
+  }
 
-  gl->Enable(GL_SCISSOR_TEST);
-  // Use a few pixels to ensure we get a clean color. The resolution for the
-  // WebGL buffer may not match the final rendered destination size, and
-  // texture filtering could interfere for single pixels. This isn't visible
-  // since the final rendering hides the edges via a vignette effect.
-  gl->Scissor(0, 0, 4, 4);
-  gl->ColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
-  // Careful with the arithmetic here. Float color 1.f is equivalent to int 255.
-  // Use the low byte of the index as the red component, and store an arbitrary
-  // magic number in green/blue. This number must match the reading code in
-  // vr_shell.cc. Avoid all-black/all-white.
-  gl->ClearColor((m_vrFrameId & 255) / 255.0f,
-                 kWebVrPosePixelMagicNumbers[0] / 255.0f,
-                 kWebVrPosePixelMagicNumbers[1] / 255.0f, 1.0f);
-  gl->Clear(GL_COLOR_BUFFER_BIT);
+  // There's two types of synchronization needed for submitting frames:
+  //
+  // - Before submitting, need to wait for the previous frame to be
+  //   pulled off the transfer surface to avoid lost frames. This
+  //   is currently a compile-time option, normally we always want
+  //   to defer this wait to increase parallelism.
+  //
+  // - After submitting, need to wait for the mailbox to be consumed,
+  //   and must remain inside the execution context while waiting.
+  //   The waitForPreviousTransferToFinish option defers this wait
+  //   until the next frame. That's more efficient, but seems to
+  //   cause wobbly framerates.
+  bool waitForPreviousTransferToFinish =
+      RuntimeEnabledFeatures::webVRExperimentalRenderingEnabled();
 
-  // Set the GL state back to what was set by the WebVR application.
-  m_renderingContext->restoreScissorEnabled();
-  m_renderingContext->restoreScissorBox();
-  m_renderingContext->restoreColorMask();
-  m_renderingContext->restoreClearColor();
+  if (waitForPreviousTransferToFinish) {
+    TRACE_EVENT0("gpu", "VRDisplay::waitForPreviousTransferToFinish");
+    while (m_pendingSubmitFrame) {
+      if (!m_submit_frame_client_binding.WaitForIncomingMethodCall()) {
+        DLOG(ERROR) << "Failed to receive SubmitFrame response";
+        break;
+      }
+    }
+  }
 
-  m_display->SubmitFrame(m_framePose.Clone());
+  RefPtr<Image> imageRef = m_renderingContext->getImage(
+      PreferAcceleration, SnapshotReasonCreateImageBitmap);
+
+  // Hardware-accelerated rendering should always be texture backed.
+  // I hope nobody is trying to do WebVR with software rendering.
+  DCHECK(imageRef->isTextureBacked());
+
+  // The AcceleratedStaticBitmapImage must be kept alive until the
+  // mailbox is used via createAndConsumeTextureCHROMIUM, the mailbox
+  // itself does not keep it alive. We must keep a reference to the
+  // image until the mailbox was consumed.
+  StaticBitmapImage* staticImage =
+      static_cast<StaticBitmapImage*>(imageRef.get());
+  staticImage->ensureMailbox();
+
+  if (waitForPreviousTransferToFinish) {
+    // Save a reference to the image to keep it alive until next frame,
+    // where we'll wait for the transfer to finish before overwriting
+    // it.
+    m_previousImage = std::move(imageRef);
+  }
+
+  // Wait for the previous render to finish, to avoid losing frames in the
+  // Android Surface / GLConsumer pair. TODO(klausw): make this tunable?
+  // Other devices may have different preferences.
+  {
+    TRACE_EVENT0("gpu", "waitForPreviousRenderToFinish");
+    while (m_pendingPreviousFrameRender) {
+      if (!m_submit_frame_client_binding.WaitForIncomingMethodCall()) {
+        DLOG(ERROR) << "Failed to receive SubmitFrame response";
+        break;
+      }
+    }
+  }
+
+  m_pendingPreviousFrameRender = true;
+  m_pendingSubmitFrame = true;
+  m_display->SubmitFrame(
+      m_vrFrameId, gpu::MailboxHolder(staticImage->mailbox(),
+                                      staticImage->syncToken(), GL_TEXTURE_2D));
+
+  // If we're not deferring the wait for transferring the mailbox,
+  // we need to wait for it now to prevent the image going out of
+  // scope before its mailbox is retrieved.
+  if (!waitForPreviousTransferToFinish) {
+    TRACE_EVENT0("gpu", "waitForCurrentTransferToFinish");
+    while (m_pendingSubmitFrame) {
+      if (!m_submit_frame_client_binding.WaitForIncomingMethodCall()) {
+        DLOG(ERROR) << "Failed to receive SubmitFrame response";
+        break;
+      }
+    }
+  }
+}
+
+void VRDisplay::OnSubmitFrameTransferred() {
+  m_pendingSubmitFrame = false;
+}
+
+void VRDisplay::OnSubmitFrameRendered() {
+  m_pendingPreviousFrameRender = false;
 }
 
 Document* VRDisplay::document() {
   return m_navigatorVR->document();
 }
 
 void VRDisplay::OnPresentChange() {
   if (m_isPresenting && !m_isValidDeviceForPresenting) {
-    VLOG(1) << __FUNCTION__ << ": device not valid, not sending event";
+    DVLOG(1) << __FUNCTION__ << ": device not valid, not sending event";
     return;
   }
   m_navigatorVR->enqueueVREvent(VRDisplayEvent::create(
       EventTypeNames::vrdisplaypresentchange, true, false, this, ""));
 }
 
 void VRDisplay::OnChanged(device::mojom::blink::VRDisplayInfoPtr display) {
   update(display);
 }
 
 void VRDisplay::OnExitPresent() {
   stopPresenting();
 }
 
 void VRDisplay::onConnected() {
   m_navigatorVR->enqueueVREvent(VRDisplayEvent::create(
       EventTypeNames::vrdisplayconnect, true, false, this, "connect"));
 }
 
 void VRDisplay::onDisconnected() {
   m_navigatorVR->enqueueVREvent(VRDisplayEvent::create(
       EventTypeNames::vrdisplaydisconnect, true, false, this, "disconnect"));
 }
 
 void VRDisplay::stopPresenting() {
   if (m_isPresenting) {
     if (!m_capabilities->hasExternalDisplay()) {
       if (m_layer.source().isHTMLCanvasElement()) {
-        auto canvas = m_layer.source().getAsHTMLCanvasElement();
-        Fullscreen::fullyExitFullscreen(canvas->document());
-        m_fullscreenCheckTimer.stop();
-        if (!m_fullscreenOrigWidth.isNull()) {
-          canvas->setInlineStyleProperty(CSSPropertyWidth,
-                                         m_fullscreenOrigWidth);
-          m_fullscreenOrigWidth = String();
-        }
-        if (!m_fullscreenOrigHeight.isNull()) {
-          canvas->setInlineStyleProperty(CSSPropertyWidth,
-                                         m_fullscreenOrigHeight);
-          m_fullscreenOrigHeight = String();
-        }
+        // TODO(klausw,crbug.com/698923): If compositor updates are
+        // suppressed, restore them here.
       } else {
         // TODO(junov, crbug.com/695497): Implement for OffscreenCanvas
       }
     } else {
       // Can't get into this presentation mode, so nothing to do here.
     }
     m_isPresenting = false;
     OnPresentChange();
   }
 
   m_renderingContext = nullptr;
   m_contextGL = nullptr;
+  m_pendingSubmitFrame = false;
+  m_pendingPreviousFrameRender = false;
 }
 
 void VRDisplay::OnActivate(device::mojom::blink::VRDisplayEventReason reason) {
   if (!m_navigatorVR->isFocused() || m_displayBlurred)
     return;
   m_navigatorVR->dispatchVRGestureEvent(VRDisplayEvent::create(
       EventTypeNames::vrdisplayactivate, true, false, this, reason));
 }
 
 void VRDisplay::OnDeactivate(
     device::mojom::blink::VRDisplayEventReason reason) {
   m_navigatorVR->enqueueVREvent(VRDisplayEvent::create(
       EventTypeNames::vrdisplaydeactivate, true, false, this, reason));
 }
 
 void VRDisplay::OnVSync(device::mojom::blink::VRPosePtr pose,
                         mojo::common::mojom::blink::TimeDeltaPtr time,
                         int16_t frameId,
                         device::mojom::blink::VRVSyncProvider::Status error) {
   switch (error) {
     case device::mojom::blink::VRVSyncProvider::Status::SUCCESS:
       break;
-    case device::mojom::blink::VRVSyncProvider::Status::RETRY:
-      m_vrVSyncProvider->GetVSync(convertToBaseCallback(
-          WTF::bind(&VRDisplay::OnVSync, wrapWeakPersistent(this))));
+    case device::mojom::blink::VRVSyncProvider::Status::CLOSING:
       return;
   }
   m_pendingVsync = false;
-  if (m_displayBlurred)
-    return;
-  if (!m_scriptedAnimationController)
-    return;
   Document* doc = this->document();
-  if (!doc)
+  if (!doc || m_displayBlurred || !m_scriptedAnimationController)
     return;
 
   WTF::TimeDelta timeDelta =
       WTF::TimeDelta::FromMicroseconds(time->microseconds);
   // Ensure a consistent timebase with document rAF.
   if (m_timebase < 0) {
     m_timebase = WTF::monotonicallyIncreasingTime() - timeDelta.InSecondsF();
   }
 
   AutoReset<bool> animating(&m_inAnimationFrame, true);
   m_framePose = std::move(pose);
   m_vrFrameId = frameId;
   m_pendingRaf = false;
   m_scriptedAnimationController->serviceScriptedAnimations(
       m_timebase + timeDelta.InSecondsF());
 }
 
 void VRDisplay::ConnectVSyncProvider() {
   if (!m_navigatorVR->isFocused() || m_vrVSyncProvider.is_bound())
     return;
   m_display->GetVRVSyncProvider(mojo::MakeRequest(&m_vrVSyncProvider));
+  m_vrVSyncProvider.set_connection_error_handler(convertToBaseCallback(
+      WTF::bind(&VRDisplay::OnVSyncConnectionError, wrapWeakPersistent(this))));
   if (m_pendingRaf && !m_displayBlurred) {
     m_pendingVsync = true;
     m_vrVSyncProvider->GetVSync(convertToBaseCallback(
         WTF::bind(&VRDisplay::OnVSync, wrapWeakPersistent(this))));
   }
 }
 
-void VRDisplay::onFullscreenCheck(TimerBase*) {
-  DCHECK(m_layer.source().isHTMLCanvasElement());
-  if (!m_isPresenting) {
-    m_fullscreenCheckTimer.stop();
-    return;
-  }
-  // TODO: This is a temporary measure to track if fullscreen mode has been
-  // exited by the UA. If so we need to end VR presentation. Soon we won't
-  // depend on the Fullscreen API to fake VR presentation, so this will
-  // become unnessecary. Until that point, though, this seems preferable to
-  // adding a bunch of notification plumbing to Fullscreen.
-  if (!Fullscreen::isCurrentFullScreenElement(
-          *m_layer.source().getAsHTMLCanvasElement())) {
-    // TODO(mthiesse): Due to asynchronous resizing, we might get kicked out of
-    // fullscreen when changing display parameters upon entering WebVR. So one
-    // time only, we reenter fullscreen after having left it; otherwise we exit
-    // presentation.
-    if (m_reenteredFullscreen) {
-      m_isPresenting = false;
-      OnPresentChange();
-      m_fullscreenCheckTimer.stop();
-      if (m_display)
-        m_display->ExitPresent();
-      return;
-    }
-    m_reenteredFullscreen = true;
-    auto canvas = m_layer.source().getAsHTMLCanvasElement();
-    Document* doc = this->document();
-    std::unique_ptr<UserGestureIndicator> gestureIndicator;
-    if (doc) {
-      gestureIndicator = WTF::wrapUnique(
-          new UserGestureIndicator(DocumentUserGestureToken::create(
-              doc, UserGestureToken::Status::PossiblyExistingGesture)));
-    }
-    Fullscreen::requestFullscreen(*canvas);
-  }
+void VRDisplay::OnVSyncConnectionError() {
+  m_vrVSyncProvider.reset();
+  ConnectVSyncProvider();
 }
 
 ScriptedAnimationController& VRDisplay::ensureScriptedAnimationController(
     Document* doc) {
   if (!m_scriptedAnimationController)
     m_scriptedAnimationController = ScriptedAnimationController::create(doc);
 
   return *m_scriptedAnimationController;
 }
 
@@ skipping 35 matching lines @@
   visitor->trace(m_stageParameters);
   visitor->trace(m_eyeParametersLeft);
   visitor->trace(m_eyeParametersRight);
   visitor->trace(m_layer);
   visitor->trace(m_renderingContext);
   visitor->trace(m_scriptedAnimationController);
   visitor->trace(m_pendingPresentResolvers);
 }
 
 }  // namespace blink