Reland of Fix bug with blank pages during navigation (patchset #1 id:1 of...

Reland of Fix bug with blank pages during navigation (patchset #1 id:1 of https://codereview.chromium.org/2200593002/ )

Reason for revert:
No dice - NaCl still crashing in
https://build.chromium.org/p/chromium.win/builders/Win7%20Tests%20%281%29/builds/55553

Original issue's description:
> Revert of Fix bug with blank pages during navigation (patchset #1 id:1 of https://codereview.chromium.org/2197783002/ )
>
> Reason for revert:
> Suspected for widespread NaCl plugin failures on waterfall since
> https://build.chromium.org/p/chromium.win/builders/Win7%20Tests%20%281%29/builds/55504
>
> Crashes with "Actual: "Plugin crashed. 'NaCl module crashed"
>
> It wasn't r408782, so I think it's gotta be this or r408781.
>
> Original issue's description:
> > Fix bug with blank pages during navigation
> >
> > This bug started after r408172.  In some situations when navigating, the
> > SetNeedsBeginFrame messages that is sent from the
> > CompositorExternalBeginFrameSource to the RenderWidgetHostView, but is
> > received by the RenderWidgetHostImpl while the RenderViewHost is swapped
> > out and before it has swapped back in.  In these cases, if this message
> > is dropped, the renderer will never tick new frames and the tab will
> > freeze.  This appears to be racy, as the renderer finds out that it is
> > visible and sends this message before the view host is swapped in.
> >
> > To fix this race, always allow the SetNeedsBeginFrame message to be
> > received while being swapped out so that the RenderWidgetHostView can be
> > in the correct state when it is swapped in.
> >
> > R=sievers@chromium.org
> > BUG=632276
> >
> > Committed: https://crrev.com/fae0fb34ab73f12a8be3493f0ec06dbbb32c7b20
> > Cr-Commit-Position: refs/heads/master@{#408787}
>
> TBR=kenrb@chromium.org,sievers@chromium.org,enne@chromium.org
> NOTRY=true
> BUG=632276
>
> Committed: https://crrev.com/ad648d7d920843e226b5f0aee2cf8e9662412413
> Cr-Commit-Position: refs/heads/master@{#408899}

TBR=kenrb@chromium.org,sievers@chromium.org,enne@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=632276

Review-Url: https://codereview.chromium.org/2195253002
Cr-Commit-Position: refs/heads/master@{#408902}

content/common/swapped_out_messages.cc

@@ -20,6 +20,8 @@ bool SwappedOutMessages::CanSendWhileSwappedOut(const IPC::Message* msg) {
     // Handled by RenderWidgetHost.
     case InputHostMsg_HandleInputEvent_ACK::ID:
     case ViewHostMsg_UpdateRect::ID:
+    // Handled by RenderWidgetHostView.
+    case ViewHostMsg_SetNeedsBeginFrames::ID:
     // Allow targeted navigations while swapped out.
     case FrameHostMsg_OpenURL::ID:
     case ViewHostMsg_Focus::ID: