Revert of Revert of Drop CreateChildFrame messages when swapping out.

Revert of Revert of Drop CreateChildFrame messages when swapping out. (patchset #1 id:1 of https://codereview.chromium.org/663183003/)

Reason for revert:
This revert was supposed to be on a branch but happened on master.

Original issue's description:
> Revert of Drop CreateChildFrame messages when swapping out. (patchset #1 id:1 of https://codereview.chromium.org/649683007/)
>
> Reason for revert:
> It broke compile since this CL relies on https://crrev.com/cce56cd951f6685a0120db63418aa7e6d3df28f2 and it isn't in this branch.
>
> Original issue's description:
> > Drop CreateChildFrame messages when swapping out.
> >
> > There is a race condition in the current state of the code where in cross-process navigation we swap the existing RenderFrameHost with a new RenderFrameHost. If the existing host sends an IPC message to create a new child frame, it arrives on the IO thread, allocates a routing id based of the existing process (p1) and does a PostTask to the UI thread. If there is a CommitPending event either executing on the UI thread or in the task queue before the task posted from the IO thread, it will end up putting the existing RenderFrameHost in swapped out state (or waiting for swapped out). When the task to create a child frame is executed after that, it creates a new RenderFrameHost, but it uses the "current" process (p2), which is different than the process that sent the message (p1). This manifests sometimes as adding duplicate routing ids to RenderProcessHost and is in general really bad bug.
> >
> > BUG=415059, 423691, 381990
> >
> > Review URL: https://codereview.chromium.org/642813007
> >
> > Cr-Commit-Position: refs/heads/master@{#299939}
> > (cherry picked from commit dcdb02fab210ec5f7b8b560075ce96d0f48f344c)
> >
> > Conflicts:
> > 	content/browser/frame_host/navigator_impl_unittest.cc
> >
> > R=creis@chromium.org
> >
> > Committed: https://chromium.googlesource.com/chromium/src/+/a6a21983b1a29ad11d30782c66d95facca65ab55
>
> TBR=creis@chromium.org
> NOTREECHECKS=true
> NOTRY=true
> BUG=415059, 423691, 381990
>
> Committed: https://crrev.com/d2c7272b80fe61a11cd2f04f17fb6caf52631010
> Cr-Commit-Position: refs/heads/master@{#300332}

TBR=creis@chromium.org,nasko@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=415059, 423691, 381990
Committed: https://crrev.com/fb22f9a029becb63e209088e6ab778457c2476c1
Cr-Commit-Position: refs/heads/master@{#300333}

[dgrogan, 2014-10-20 21:25:38]

Created Revert of Revert of Drop CreateChildFrame messages when swapping out.

[commit-bot: I haz the power, 2014-10-20 21:29:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/667813002/1

[commit-bot: I haz the power, 2014-10-20 21:32:57]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-20 21:33:37]

Patchset 1 (id:??) landed as
https://crrev.com/fb22f9a029becb63e209088e6ab778457c2476c1
Cr-Commit-Position: refs/heads/master@{#300333}