Move SetRootLayer into base.

Collapse root layer implementation into a common implementation. One
subtle difference is that the root layer on the child root frames is now
set to null during destruction, I believe this is more correct.

BUG=1097816

Change-Id: I5556680d0170280918a21027ff602c37b16d5598
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2542757
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828939}

third_party/blink/renderer/core/exported/web_view_impl.cc

@@ -3431,6 +3431,10 @@ bool WebViewImpl::TabsToLinks() const {
 }
 
 void WebViewImpl::DidChangeRootLayer(bool root_layer_exists) {
+  // The Layer is removed when the main frame's `Document` changes. It also is
+  // removed when the whole `LocalFrame` goes away, in which case we don't
+  // need to DeferMainFrameUpdate() as we will do so if a local MainFrame is
+  // attached in the future.
   if (!MainFrameImpl()) {
     DCHECK(!root_layer_exists);
     return;

third_party/blink/renderer/core/exported/web_view_impl.h

@@ -498,6 +498,9 @@ class CORE_EXPORT WebViewImpl final : public WebView,
   // code should eventually move out of WebView into somewhere else.
   void ApplyViewportChanges(const ApplyViewportChangesArgs& args);
 
+  // Indication that the root layer for the main frame widget has changed.
+  void DidChangeRootLayer(bool root_layer_exists);
+
   // This method is used for testing.
   // Resizes the unscaled (page scale = 1.0) visual viewport. Normally the
   // unscaled visual viewport is the same size as the main frame. The passed
@@ -596,8 +599,6 @@ class CORE_EXPORT WebViewImpl final : public WebView,
 
   float DeviceScaleFactor() const;
 
-  void DidChangeRootLayer(bool root_layer_exists);
-
   LocalFrame* FocusedLocalFrameInWidget() const;
 
   // Clear focus and text input state of the page. If there was a focused

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

@@ -2174,6 +2174,33 @@ void WebFrameWidgetBase::RequestAnimationAfterDelay(
   }
 }
 
+void WebFrameWidgetBase::SetRootLayer(scoped_refptr<cc::Layer> layer) {
+  if (!View()->does_composite()) {
+    DCHECK(ForMainFrame());
+    DCHECK(!layer);
+    return;
+  }
+
+  // Set up some initial state before we are setting the layer.
+  if (ForSubframe() && layer) {
+    // Child local roots will always have a transparent background color.
+    widget_base_->LayerTreeHost()->set_background_color(SK_ColorTRANSPARENT);
+    // Pass the limits even though this is for subframes, as the limits will
+    // be needed in setting the raster scale.
+    SetPageScaleStateAndLimits(1.f, false /* is_pinch_gesture_active */,
+                               View()->MinimumPageScaleFactor(),
+                               View()->MaximumPageScaleFactor());
+  }
+
+  bool root_layer_exists = !!layer;
+  widget_base_->LayerTreeHost()->SetRootLayer(std::move(layer));
+
+  // Notify the WebView that we did set a layer.
+  if (ForMainFrame()) {
+    View()->DidChangeRootLayer(root_layer_exists);
+  }
+}
+
 void WebFrameWidgetBase::RequestAnimationAfterDelayTimerFired(TimerBase*) {
   if (client_)
     client_->ScheduleAnimation();

third_party/blink/renderer/core/frame/web_frame_widget_base.h

@@ -147,6 +147,7 @@ class CORE_EXPORT WebFrameWidgetBase
   void SetOverscrollBehavior(
       const cc::OverscrollBehavior& overscroll_behavior) final;
   void RequestAnimationAfterDelay(const base::TimeDelta&) final;
+  void SetRootLayer(scoped_refptr<cc::Layer>) override;
   void RegisterSelection(cc::LayerSelection selection) final;
   void RequestDecode(const cc::PaintImage&,
                      base::OnceCallback<void(bool)>) final;

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

@@ -454,25 +454,6 @@ PaintLayerCompositor* WebFrameWidgetImpl::Compositor() const {
   return frame->GetDocument()->GetLayoutView()->Compositor();
 }
 
-void WebFrameWidgetImpl::SetRootLayer(scoped_refptr<cc::Layer> layer) {
-  if (!layer) {
-    // This notifies the WebFrameWidgetImpl that its LocalFrame tree is being
-    // detached.
-    return;
-  }
-
-  // WebFrameWidgetImpl is used for child frames, which always have a
-  // transparent background color.
-  widget_base_->LayerTreeHost()->set_background_color(SK_ColorTRANSPARENT);
-  // Pass the limits even though this is for subframes, as the limits will
-  // be needed in setting the raster scale.
-  SetPageScaleStateAndLimits(1.f, false /* is_pinch_gesture_active */,
-                             View()->MinimumPageScaleFactor(),
-                             View()->MaximumPageScaleFactor());
-
-  widget_base_->LayerTreeHost()->SetRootLayer(layer);
-}
-
 void WebFrameWidgetImpl::DidCreateLocalRootView() {
   // If this WebWidget still hasn't received its size from the embedder, block
   // the parser. This is necessary, because the parser can cause layout to

third_party/blink/renderer/core/frame/web_frame_widget_impl.h

@@ -50,10 +50,6 @@
 #include "third_party/blink/renderer/platform/heap/self_keep_alive.h"
 #include "third_party/blink/renderer/platform/wtf/hash_set.h"
 
-namespace cc {
-class Layer;
-}
-
 namespace blink {
 class Element;
 class PaintLayerCompositor;
@@ -101,7 +97,6 @@ class WebFrameWidgetImpl final : public WebFrameWidgetBase {
       const VisualProperties& visual_properties) override;
 
   // FrameWidget overrides:
-  void SetRootLayer(scoped_refptr<cc::Layer>) override;
   bool ShouldHandleImeEvents() override;
 
   // WidgetBaseClient overrides:

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

@@ -114,16 +114,6 @@ bool WebViewFrameWidget::ScrollFocusedEditableElementIntoView() {
   return web_view_->ScrollFocusedEditableElementIntoView();
 }
 
-void WebViewFrameWidget::SetRootLayer(scoped_refptr<cc::Layer> root_layer) {
-  if (!web_view_->does_composite()) {
-    DCHECK(!root_layer);
-    return;
-  }
-  cc::LayerTreeHost* layer_tree_host = widget_base_->LayerTreeHost();
-  layer_tree_host->SetRootLayer(root_layer);
-  web_view_->DidChangeRootLayer(!!root_layer);
-}
-
 WebInputEventResult WebViewFrameWidget::HandleGestureEvent(
     const WebGestureEvent& event) {
   if (!web_view_->Client() || !web_view_->Client()->CanHandleGestureEvent()) {

third_party/blink/renderer/core/frame/web_view_frame_widget.h

@@ -73,7 +73,6 @@ class CORE_EXPORT WebViewFrameWidget : public WebFrameWidgetBase {
       const VisualProperties& visual_properties) override;
 
   // FrameWidget overrides:
-  void SetRootLayer(scoped_refptr<cc::Layer>) override;
   bool ShouldHandleImeEvents() override;
 
   // WidgetBaseClient overrides: