Turn on AreCrossProcessFramesPossible by default.

content/browser/frame_host/render_widget_host_view_guest.cc

 // Copyright 2014 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/frame_host/render_widget_host_view_guest.h"
 
 #include <utility>
 
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
@@ skipping 337 matching lines @@
   return rwhv->GetNativeViewAccessible();
 }
 
 void RenderWidgetHostViewGuest::UpdateCursor(const WebCursor& cursor) {
   // InterstitialPages are not WebContents so we cannot intercept
   // ViewHostMsg_SetCursor for interstitial pages in BrowserPluginGuest.
   // All guest RenderViewHosts have RenderWidgetHostViewGuests however,
   // and so we will always hit this code path.
   if (!guest_)
     return;
+  // TODO(creis): This is wrong.  Should check for OOPIF webview mode instead.

[alexmos, 2017/02/04 02:03:01]

I actually think this is ok.  The description in the CL that introduced this,
https://codereview.chromium.org/1845083002, seems to imply that this should
trigger based on whether the input event router is installed, which James
confirmed should be triggered by AreCrossProcessFramesPossible().  I chatted
with Lucas, and he also agreed that this call is ok as is.

[Charlie Reis, 2017/02/13 22:02:49]

Acknowledged.

   if (SiteIsolationPolicy::AreCrossProcessFramesPossible()) {
     RenderWidgetHostViewBase* rwhvb = GetOwnerRenderWidgetHostView();
     if (rwhvb)
       rwhvb->UpdateCursor(cursor);
   } else {
     guest_->SendMessageToEmbedder(base::MakeUnique<BrowserPluginMsg_SetCursor>(
         guest_->browser_plugin_instance_id(), cursor));
   }
 }
 
@@ skipping 279 matching lines @@
         gesture_event.data.scrollUpdate.inertialPhase ==
             blink::WebGestureEvent::MomentumPhase) {
       return;
     }
     host_->ForwardGestureEvent(gesture_event);
     return;
   }
 }
 
 }  // namespace content