[analyzer] Faster relative-path-if-inside-same-dir function for `AbstractDartSdk.getPath`

AbstractDartSdk._getPath has some "phases" trying to determine a
"dart import uri" from a File.
One of these phases checks if the given file is inside a directory that
one of the known sdk platforms is inside, thus allowing us to construct
a uri from there.
For instance if we know that `/a/b/c/d/e.dart` is called
`dart:foo/e.dart` and we’re presented with `/a/b/c/d/f.dart` we’ll
figure out that it’s called `dart:foo/f.dart`.
The code for this is very simple, but very inefficient.

This CL makes it more efficient.

This is only applicable when analyzing with the flutter platform.

The below benchmarks show a ~7 to ~33% improvement depending on what's
being analyzed. It's all done via `dart analyze` where the first run
has been discarded so everything is in cache.

Running on `rwf-materials`:

```
Before:
real    1m54.491s
real    1m55.969s
real    1m53.802s

Now:
real    1m16.348s
real    1m17.570s
real    1m17.149s

Difference at 95.0% confidence
        -37.7317 +/- 1.06819
        -32.8805% +/- 0.930855%
        (Student's t, pooled s = 0.471277)
```

Running on "flutter gallery":

```
Before:
real    0m2.836s
real    0m2.783s
real    0m2.718s

Now:
real    0m2.478s
real    0m2.492s
real    0m2.451s

Difference at 95.0% confidence
        -0.305333 +/- 0.10044
        -10.9872% +/- 3.61426%
        (Student's t, pooled s = 0.0443133)
```

Running on "flutter-wonderous-app":

```
Before:
real    0m2.019s
real    0m1.999s
real    0m1.984s

Now:
real    0m1.863s
real    0m1.821s
real    0m1.856s

Difference at 95.0% confidence
        -0.154 +/- 0.0457455
        -7.69743% +/- 2.28652%
        (Student's t, pooled s = 0.0201825)
```

Running on "flutter gallery" and "flutter-wonderous-app" at the same time:

```
Before:
real    0m3.446s
real    0m3.407s
real    0m3.431s

Now:
real    0m2.993s
real    0m2.965s
real    0m3.008s

Difference at 95.0% confidence
        -0.439333 +/- 0.0470921
        -12.816% +/- 1.37375%
        (Student's t, pooled s = 0.0207766)
```

Change-Id: I13e81e96312d9cb5ad2a8244a0cb7722a49c4460
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/282280
Commit-Queue: Jens Johansen <jensj@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
4 files changed
tree: dd929aecd35a1b9898ebd4350639716b766216b0
  1. .dart_tool/
  2. .github/
  3. benchmarks/
  4. build/
  5. docs/
  6. pkg/
  7. runtime/
  8. samples/
  9. sdk/
  10. tests/
  11. third_party/
  12. tools/
  13. utils/
  14. .clang-format
  15. .gitattributes
  16. .gitconfig
  17. .gitignore
  18. .gn
  19. .mailmap
  20. .style.yapf
  21. .vpython
  22. AUTHORS
  23. BUILD.gn
  24. CHANGELOG.md
  25. codereview.settings
  26. CONTRIBUTING.md
  27. DEPS
  28. LICENSE
  29. OWNERS
  30. PATENT_GRANT
  31. PRESUBMIT.py
  32. README.dart-sdk
  33. README.md
  34. sdk_args.gni
  35. SECURITY.md
  36. WATCHLISTS
README.md

Dart

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