This reverts commit decf5750.

Reason for revert: broken layout tests

Original change's description:
> [runtime] Store hash code in length field
> 
> Store the hash code in 21 bits of the length field.
> 
> Change the GetIdentityHash API to be unhandlified, since there's no
> property lookup anymore.
> 
> Update js/ and test/ to match new API and expections.
> 
> Bug: 
> Change-Id: I8dc75de4021f59e79b45f3f38ec997c3b3687b24
> Reviewed-on: https://chromium-review.googlesource.com/589688
> Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#47259}

TBR=ulan@chromium.org,jkummerow@chromium.org,mstarzinger@chromium.org,cbruni@chromium.org,gsathya@chromium.org

Change-Id: I32db9c20a51b2401464924cafea502628a0d0b92
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/609322Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47260}