Revert "Use chunks in trace event buffers"

This reverts commit cb13e0a5455c86507e493498bb232e98467333c1 because
of unit test failure (though try bots passed).

> Use chunks in trace event buffers
>
> Separated from https://codereview.chromium.org/23799005/.
>
> Chunks are fixed sized arrays of TraceEvents in trace event buffers.
> Each thread borrows a chunk from the buffer, adds thread-local events
> into the chunk without locking, and returns the chunk when it is full.
>
> TraceLog also gets a chunk from the buffer for events that are not
> suitable to use thread-local buffer.
>
> With the chunks, TraceEvent never copies except when the trace buffer
> is cloned.
>
> Changed |flush_count_| to |generation| which indicates the version of
> the central TraceBuffer. If a thread failed to flush in the last flush,
> it may still hold a TraceBufferChunk from the original TraceBuffer.
> |generation| controls the thread not to return the chunk to the current
> TraceBuffer.
>
> This is preparation for the new design for X events which exposes
> TraceEventHandle through TRACE_EVENT_API.
>
> BUG=trace-viewer:142
> TEST=Existing TraceEventTestFixture.* tests
> TEST=TraceEventTestFixture.TraceBufferRingBuffer*
>
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=227783

NOTRY=true
TBR=msw

Review URL: https://codereview.chromium.org/26444006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227816 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227816