encoding/json: apply conventional error handling in decoder

name                            old time/op    new time/op    delta
CodeEncoder-12                    1.89ms ± 1%    1.91ms ± 0%   +1.16%  (p=0.000 n=20+19)
CodeMarshal-12                    2.09ms ± 1%    2.12ms ± 0%   +1.63%  (p=0.000 n=17+18)
CodeDecoder-12                    8.43ms ± 1%    8.32ms ± 1%   -1.35%  (p=0.000 n=18+20)
UnicodeDecoder-12                  399ns ± 0%     339ns ± 0%  -15.00%  (p=0.000 n=20+19)
DecoderStream-12                   281ns ± 1%     231ns ± 0%  -17.91%  (p=0.000 n=20+16)
CodeUnmarshal-12                  9.35ms ± 2%    9.15ms ± 2%   -2.11%  (p=0.000 n=20+20)
CodeUnmarshalReuse-12             8.41ms ± 2%    8.29ms ± 2%   -1.34%  (p=0.000 n=20+20)
UnmarshalString-12                81.2ns ± 2%    74.0ns ± 4%   -8.89%  (p=0.000 n=20+20)
UnmarshalFloat64-12               71.1ns ± 2%    64.3ns ± 1%   -9.60%  (p=0.000 n=20+19)
UnmarshalInt64-12                 60.6ns ± 2%    53.2ns ± 0%  -12.28%  (p=0.000 n=18+18)
Issue10335-12                     96.9ns ± 0%    87.7ns ± 1%   -9.52%  (p=0.000 n=17+20)
Unmapped-12                        247ns ± 4%     231ns ± 3%   -6.34%  (p=0.000 n=20+20)
TypeFieldsCache/MissTypes1-12     11.1µs ± 0%    11.1µs ± 0%     ~     (p=0.376 n=19+20)
TypeFieldsCache/MissTypes10-12    33.9µs ± 0%    33.8µs ± 0%   -0.32%  (p=0.000 n=18+9)

name                            old speed      new speed      delta
CodeEncoder-12                  1.03GB/s ± 1%  1.01GB/s ± 0%   -1.15%  (p=0.000 n=20+19)
CodeMarshal-12                   930MB/s ± 1%   915MB/s ± 0%   -1.60%  (p=0.000 n=17+18)
CodeDecoder-12                   230MB/s ± 1%   233MB/s ± 1%   +1.37%  (p=0.000 n=18+20)
UnicodeDecoder-12               35.0MB/s ± 0%  41.2MB/s ± 0%  +17.60%  (p=0.000 n=20+19)
CodeUnmarshal-12                 208MB/s ± 2%   212MB/s ± 2%   +2.16%  (p=0.000 n=20+20)

name                            old alloc/op   new alloc/op   delta
Issue10335-12                       184B ± 0%      184B ± 0%     ~     (all equal)
Unmapped-12                         216B ± 0%      216B ± 0%     ~     (all equal)

name                            old allocs/op  new allocs/op  delta
Issue10335-12                       3.00 ± 0%      3.00 ± 0%     ~     (all equal)
Unmapped-12                         4.00 ± 0%      4.00 ± 0%     ~     (all equal)

Change-Id: I4b1a87a205da2ef9a572f86f85bc833653c61570
Reviewed-on: https://go-review.googlesource.com/98440
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>