Revert "Remove window.postMessage(message, transferables, targetOrigin) legacy overload"

This reverts commits a91dd1d7611e879f8d03bf533c45fa229ed7246d and
48caa2cebaf1723dcfd8665e4859d90e2b55f2a2.

In addition:
 * Update the deprecation message for M55 removal.
 * Exclude changes to postMessage calls outside of tests, as those might
   otherwise trigger the deprecation message.

BUG=425896,649157
TBR=sigbjornf@opera.com,haraken@chromium.org
NOTRY=true
NOPRESUBMIT=true

Review-Url: https://codereview.chromium.org/2362693004
Cr-Commit-Position: refs/branch-heads/2840@{#509}
Cr-Branched-From: 1ae106dbab4bddd85132d5b75c670794311f4c57-refs/heads/master@{#414607}
5 files changed