This reverts commit 06ff9e97.

Reason for revert: Breaks deopt information with --prof. Deopts no longer show up properly in the logfile / profview

Original change's description:
> [logging] Use OFStream for log events
> 
> This simplifies a few operations and removes the size limitations
> implied by the message buffer used.
> 
> Change-Id: I8b873a0ffa399a037ff5c2501ba4b68158810968
> Reviewed-on: https://chromium-review.googlesource.com/724285
> Commit-Queue: Camillo Bruni <cbruni@chromium.org>
> Reviewed-by: Adam Klein <adamk@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#48766}

TBR=adamk@chromium.org,cbruni@chromium.org

Change-Id: I290da0b2472ad0e765b765b26bdde334253376e3
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/730164Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48776}