Make RenderFrameHostImpl::GetRenderWidgetHost() always return an object

content/browser/frame_host/render_frame_host_impl.h

Index: content/browser/frame_host/render_frame_host_impl.h
diff --git a/content/browser/frame_host/render_frame_host_impl.h b/content/browser/frame_host/render_frame_host_impl.h
index 420a2c2795d7512d3ac241213dc4854290d45737..86b77054601c52ff274ae87b5132c0b407a356b9 100644
--- a/content/browser/frame_host/render_frame_host_impl.h
+++ b/content/browser/frame_host/render_frame_host_impl.h
@@ -252,12 +252,23 @@ class CONTENT_EXPORT RenderFrameHostImpl : public RenderFrameHost,
   // TODO(clamy): Remove this once PlzNavigate ships.
   void set_is_loading(bool is_loading) { is_loading_ = is_loading; }
 
-  // This returns the RenderFrameHost's owned RenderWidgetHost if it has one,
-  // or else it returns nullptr.
-  // If the RenderFrameHost is the page's main frame, this returns instead a
-  // pointer to the RenderViewHost (which inherits RenderWidgetHost).
+  // Returns the RenderWidgetHostImpl attached to this frame or the nearest

[Charlie Reis, 2016/05/27 22:50:28]

nit: owned by this frame or its nearest

(Is that accurate enough?  I realize the root widget is technically still owned
by the RVH, but it kind of seems like every frame is attached to a widget.)

[kenrb, 2016/05/30 19:39:54]

I think it's accurate enough. Even though technically the root frame doesn't
(yet) own its widget, it still has its render_widget_host_ pointer set as if it
does.

+  // ancestor frame, which could potentially be the root. For most input
+  // and rendering related purposes, GetView() should be preferred and
+  // RenderWidgetHostViewBase methods used. Unlike GetView(),
+  // GetRenderWidgetHost() will not return a nullptr.

[Charlie Reis, 2016/05/27 22:50:28]

nit: nullptr after a renderer crash.

(Helpful to give more context about when GetView is null.)

[kenrb, 2016/05/30 19:39:54]

Done.

+  //
+  // This method crashes if this RenderFrameHostImpl is not attached to the
+  // frame tree.

[Charlie Reis, 2016/05/27 22:50:28]

nit: if this RenderFrameHost has no RenderWidgetHost in any of its ancestors,
which could happen if it has been detached from the frame tree.

[kenrb, 2016/05/30 19:39:54]

Done.

   RenderWidgetHostImpl* GetRenderWidgetHost();
 
+  // Returns true if this is a top-level frame, or if this frame's RenderFrame
+  // is in a different process from its parent frame. Local roots are
+  // distinguished by owning a RenderWidgetHost, which manages input events
+  // and painting for this frame and its contiguous local subtree in the
+  // renderer process.
+  bool IsLocalRoot();

[Charlie Reis, 2016/05/27 22:50:28]

nit: Let's move this above GetRenderWidgetHost(), since it's a useful concept
for understanding the comment on GetRenderWidgetHost().

This can also be is_local_root() and inlined into the .h file, since it's
trivial and not virtual.

[kenrb, 2016/05/30 19:39:54]

Done.

+
   GlobalFrameRoutingId GetGlobalFrameRoutingId();
 
   // This function is called when this is a swapped out RenderFrameHost that