Reland of [tracing] Fix, simplify and speed up accounting of TraceEvent memory overhead

Reland of [tracing] Fix, simplify and speed up accounting of TraceEvent memory overhead (patchset #2 id:110001 of https://codereview.chromium.org/1258903003/ )

Reason for revert:
Reverting did not solve crbug.com/516056

Original issue's description:
> Revert of [tracing] Fix, simplify and speed up accounting of TraceEvent memory overhead (patchset #4 id:60001 of https://codereview.chromium.org/1251203003/ )
>
> Reason for revert:
> Speculative revert for https://code.google.com/p/chromium/issues/detail?id=516056
>
> Original issue's description:
> > [tracing] Fix, simplify and speed up accounting of TraceEvent memory overhead
> >
> > So far the accounting of TraceEvent memory overhead worked as follows:
> >  - Each TraceEvent keeps a cache of its own overhead.
> >  - The TraceBufferChunk (which is approx an array of 64 TraceEvent)
> >    keeps a cache of the all 64 TraceEvent, but only when completelly
> >    filled.
> >
> > This is sub-optimal because:
> >  - There can be many TraceEvent(s), 10k-100k in a bulky 30s trace:
> >    when memory-infra is enabled, this causes a cost of several MB to
> >    keep the aforementioned per-TraceEvent caches.
> >  - Every time we have to estimate the size of a non-completely-full
> >    TraceBufferChunk, we still have to loop over their individual caches.
> >  - Least but not last, turns out that the current accounting is just
> >    wrong, as we ended up counting the sizeof(TraceEvent) both in
> >    TraceBufferChunk and in the individual TraceEvent.
> >
> > This CL improves the situation as follows:
> >  - The per-TraceEvent cache is dropped. Much less memory is used.
> >  - The TraceBufferChunk still keeps a cache, but its cache is used in a
> >    smarter way and not just when it is full. We simply remember how many
> >    TraceEvent(s) we estimated in the previous pass and then estimate just
> >    the missing ones.
> >  - The double accounting issue is fixed, as now we count TraceEvent(s)
> >    only in TraceBufferChunk.
> >
> > BUG=512383
> >
> > Committed: https://crrev.com/b2ae97fb331cbad132a8e1aad9a25441fde75048
> > Cr-Commit-Position: refs/heads/master@{#340005}
>
> TBR=dsinclair@chromium.org,primiano@chromium.org
> BUG=512383
>
> Committed: https://crrev.com/8f329fc15f5fa64f64308244266a304c122a2868
> Cr-Commit-Position: refs/heads/master@{#341910}

TBR=dsinclair@chromium.org,primiano@chromium.org,dyen@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=512383
Committed: https://crrev.com/20a0811a97a03cf3db4c98a96cefb5cad6070026
Cr-Commit-Position: refs/heads/master@{#342157}

[oystein (OOO til 10th of July), 2015-08-06 18:39:36]

Created Reland of [tracing] Fix, simplify and speed up accounting of TraceEvent
memory overhead

[commit-bot: I haz the power, 2015-08-06 18:40:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1265393007/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1265393007/1

[commit-bot: I haz the power, 2015-08-06 18:41:55]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-06 18:42:38]

Patchset 1 (id:??) landed as
https://crrev.com/20a0811a97a03cf3db4c98a96cefb5cad6070026
Cr-Commit-Position: refs/heads/master@{#342157}