Make LoadLog refcounted-thread safe....

Make LoadLog refcounted-thread safe.

This also backs out r26610 (these are the changes to host_resolver_impl.cc), since that code is no longer necessary if LoadLog is refcounted thread safe.

LoadLog itself is not thread safe -- however making its refcounting threadsafe simplifies passing it across thread boundaries.

Initially I had avoided doing this, and instead was trying to be very careful in when callers would AddRef/Release to avoid races.
This approach however turned out to be fragile, and it was difficult to chase down all of the dependencies (they just kept popping up).
So now I am changing that decision, and opting for the simpler approach which will be much more robust.

The performance impact should be negligable.

BUG=22272
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=30525

[Timur Iskhodzhanov, 2009-10-29 21:01:56]

http://codereview.chromium.org/347021/diff/1/3
File net/base/load_log.h (right):

http://codereview.chromium.org/347021/diff/1/3#newcode19
Line 19: // that it can be easily passed between threads.
The comment is a bit confusing.
You can pass any not-threadsafe object between threads provided you do it with a
proper external synchronization.

I guess "it can be safely addref'ed/released from different threads" is what
you've meant

[eroman, 2009-10-29 21:04:52]

http://codereview.chromium.org/347021/diff/1/3
File net/base/load_log.h (right):

http://codereview.chromium.org/347021/diff/1/3#newcode19
Line 19: // that it can be easily passed between threads.
On 2009/10/29 21:01:56, Timur Iskhodzhanov wrote:
> The comment is a bit confusing.
> You can pass any not-threadsafe object between threads provided you do it with
a
> proper external synchronization.
> 
> I guess "it can be safely addref'ed/released from different threads" is what
> you've meant

Done.

Changed the comment to:

// Note that LoadLog is NOT THREADSAFE, however it is RefCountedThreadSafe so
// that it can be AddRef() / Release() across threads.

[Timur Iskhodzhanov, 2009-10-29 21:06:29]

LGTM