code review 5647051: In json.NewDecoder: if the paramter is also a io.ByteRe...

In json.NewDecoder: if the paramter is also a io.ByteReader, then only read
one byte each time to avoid "over-feeding".

Added a test case to test if the Decoder will over feeding. (Nearly a
verbatim copy from jdnurmi@qwe.cc, the reporter of issue 1955)

The performance using ReadByte on BenchmarkCodeDecoder is 1.6M/s; while the
old version is about 1.65M/s. This change approximately hurts the performance
by 4%. Test environment:
        - CPU: Intel(R) Core(TM) i5 CPU M 460 @ 2.53GHz
        - Memory: 6GB

Fixes issue 1955

[Nan Deng, 2012-02-08 11:34:07]

Hello golang-dev@googlegroups.com (cc: golang-dev@googlegroups.com,
iant@golang.org, rsc@golang.org),

I'd like you to review this change to
https://go.googlecode.com/hg/

[r2, 2012-02-08 11:38:21]

Maybe after Go 1.

-rob

[rsc, 2012-02-08 15:23:01]

I agree.  This is a bigger change than I'm willing
to make to such a core package this close to Go 1.
I will send out a CL to document the buffering for now.
Please remind us about this CL after Go 1 is out.

Thanks.
Russ

[Nan Deng, 2012-02-08 23:34:09]

Russ Cox wrote, On 02/08/2012 10:23 AM:
> I agree.  This is a bigger change than I'm willing
> to make to such a core package this close to Go 1.
> I will send out a CL to document the buffering for now.
> Please remind us about this CL after Go 1 is out.
>

Sure. I will send another mail to this thread after Go 1 is out. In the 
Meantime, I will keep optimizing the code to make it faster.

BTW, I am really exciting to hear that Go 1 is near. We are expecting it 
for (not too) long time.

Thanks,
-Nan
> Thanks.
> Russ
>