This reverts commit 69c8f16d.

Reason for revert: Causing crashes on Clusterfuzz - http://crbug.com/747154

BUG=chromium:747154

Original change's description:
> [Turbofan] Merged the OSR phase into the graph building phase.
> 
> Now the OSR phase is only used when OSRing from the ast graph builder.
> When OSRing from Turbofan, the implementation is now in the graph
> building phase, at the beginning of the VisitBytecode function.
> We are no longer generating any OSRLoopEntry or OSRNormalEntry nodes,
> nor nodes for the possible code of the OSRed function which is before
> the OSRed loops.
> 
> The trimming and reducing of the OSR phase is not done either. This
> change in the way the way the OSR is done enabled to remove the
> workaround to the bug mentioned below.
> 
> Bug: v8:6112
> Bug: v8:6518
> Change-Id: I1c9231810b923486d55ea618d550d981d695d797
> Reviewed-on: https://chromium-review.googlesource.com/543042
> Commit-Queue: Alexandre Talon <alexandret@google.com>
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#46801}

TBR=rmcilroy@chromium.org,mstarzinger@chromium.org,leszeks@chromium.org,alexandret@google.com

Change-Id: Ifa9bf5d86e888a47cad7fb10446b36fda5029604
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:6112, v8:6518
Reviewed-on: https://chromium-review.googlesource.com/581288Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46817}