Optimize base::EscapeJSONString for ASCII inputs.
Most of the strings passed to this function are ASCII-only and
don't even need escaping. This CL provides fast-paths for these
cases.
This speeds up the generation of many JSON files written by GN.
For example, on a large Fuchsia build plan, this saves about 4
seconds while generating identical JSON outputs:
```
$ hyperfine --runs=5 '/tmp/gn1 gen --ide=json out/default --export-rust-project --export-compile-commands' '/tmp/gn3 gen --ide=json out/default --export-rust-project --export-compile-commands'
Benchmark 1: /tmp/gn1 gen --ide=json out/default --export-rust-project --export-compile-commands
Time (mean ± σ): 28.883 s ± 0.836 s [User: 117.852 s, System: 42.476 s]
Range (min … max): 27.694 s … 29.916 s 5 runs
Benchmark 2: /tmp/gn2 gen --ide=json out/default --export-rust-project --export-compile-commands
Time (mean ± σ): 24.829 s ± 0.590 s [User: 112.068 s, System: 42.400 s]
Range (min … max): 23.879 s … 25.296 s 5 runs
Summary
'/tmp/gn3 gen --ide=json out/default --export-rust-project --export-compile-commands' ran
1.16 ± 0.04 times faster than '/tmp/gn1 gen --ide=json out/default --export-rust-project --export-compile-commands'
```
Change-Id: I7f678f898a9e7f1d271ef8cb47ea77bb6d22800c
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/16040
Commit-Queue: David Turner <[email protected]>
Reviewed-by: Takuto Ikuta <[email protected]>
