RenderWidgetHostViewChildFrame's called a virtual in its ctor.

content/browser/renderer_host/render_widget_host_view_aura.cc

 // Copyright (c) 2012 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 "content/browser/renderer_host/render_widget_host_view_aura.h"
 
 #include <set>
 #include <utility>
 
 #include "base/auto_reset.h"
@@ skipping 421 matching lines @@
       window_(nullptr),
       in_shutdown_(false),
       in_bounds_changed_(false),
       is_fullscreen_(false),
       popup_parent_host_view_(nullptr),
       popup_child_host_view_(nullptr),
       is_loading_(false),
       has_composition_text_(false),
       accept_return_character_(false),
       begin_frame_source_(nullptr),
+      needs_begin_frames_(false),
+      added_frame_observer_(false),
       synthetic_move_sent_(false),
       cursor_visibility_state_in_renderer_(UNKNOWN),
 #if defined(OS_WIN)
       legacy_render_widget_host_HWND_(nullptr),
       legacy_window_destroyed_(false),
       virtual_keyboard_requested_(false),
 #endif
       has_snapped_to_boundary_(false),
       is_guest_view_hack_(is_guest_view_hack),
       set_focus_on_mouse_down_or_key_event_(false),
@@ skipping 256 matching lines @@
 
   NOTIMPLEMENTED();
   return static_cast<gfx::NativeViewAccessible>(NULL);
 }
 
 ui::TextInputClient* RenderWidgetHostViewAura::GetTextInputClient() {
   return this;
 }
 
 void RenderWidgetHostViewAura::SetNeedsBeginFrames(bool needs_begin_frames) {
+  needs_begin_frames_ = needs_begin_frames;
+  UpdateNeedsBeginFramesInternal();
+}
+
+void RenderWidgetHostViewAura::UpdateNeedsBeginFramesInternal() {
   if (!begin_frame_source_)
     return;
 
-  if (needs_begin_frames)
+  if (added_frame_observer_ == needs_begin_frames_)
+    return;
+
+  if (needs_begin_frames_)
     begin_frame_source_->AddObserver(this);
   else
     begin_frame_source_->RemoveObserver(this);
+  added_frame_observer_ = needs_begin_frames_;
 }
 
 void RenderWidgetHostViewAura::OnBeginFrame(
     const cc::BeginFrameArgs& args) {
   host_->Send(new ViewMsg_BeginFrame(host_->GetRoutingID(), args));
   last_begin_frame_args_ = args;
 }
 
 const cc::BeginFrameArgs& RenderWidgetHostViewAura::LastUsedBeginFrameArgs()
     const {
@@ skipping 2185 matching lines @@
   host_->Send(new ViewMsg_ReclaimCompositorResources(
       host_->GetRoutingID(), compositor_frame_sink_id, is_swap_ack, resources));
 }
 
 void RenderWidgetHostViewAura::DelegatedFrameHostOnLostCompositorResources() {
   host_->ScheduleComposite();
 }
 
 void RenderWidgetHostViewAura::SetBeginFrameSource(
     cc::BeginFrameSource* source) {
-  bool needs_begin_frames = host_->needs_begin_frames();
-  if (begin_frame_source_ && needs_begin_frames)
+  if (begin_frame_source_ && added_frame_observer_) {
     begin_frame_source_->RemoveObserver(this);
+    added_frame_observer_ = false;
+  }
   begin_frame_source_ = source;
-  if (begin_frame_source_ && needs_begin_frames)
-    begin_frame_source_->AddObserver(this);
+  UpdateNeedsBeginFramesInternal();
 }
 
 bool RenderWidgetHostViewAura::IsAutoResizeEnabled() const {
   return host_->auto_resize_enabled();
 }
 
 void RenderWidgetHostViewAura::OnDidNavigateMainFrameToNewPage() {
   ui::GestureRecognizer::Get()->CancelActiveTouches(window_);
 }
 
@@ skipping 99 matching lines @@
           ->GetTextSelection(focused_view)
           ->GetSelectedText(&selected_text)) {
     // Set the CLIPBOARD_TYPE_SELECTION to the ui::Clipboard.
     ui::ScopedClipboardWriter clipboard_writer(ui::CLIPBOARD_TYPE_SELECTION);
     clipboard_writer.WriteText(selected_text);
   }
 #endif  // defined(USE_X11) && !defined(OS_CHROMEOS)
 }
 
 }  // namespace content