Bump pub to 8f5ab7b1aba3b9f66b56246d77e167990339d317

Changes:
```
> git log --format="%C(auto) %h %s" dcb6aba..8f5ab7b
 https://dart.googlesource.com/pub.git/+/8f5ab7b1 Avoid raceconditions in `global activate`, `run` and `global run` (#3285)
 https://dart.googlesource.com/pub.git/+/6e03ec02 Support multiple packages in 'dart pub add' (#3283)
 https://dart.googlesource.com/pub.git/+/1a298f4d Fix --verbose doc, and accept verboseness setting from embedder (#3279)
 https://dart.googlesource.com/pub.git/+/5bda798c Avoid race condition for hosted source on package extraction (#3277)
 https://dart.googlesource.com/pub.git/+/17c5addb Error on acquireDependencies when the root pubspec has an unknown sdk in the environment. (#3271)
 https://dart.googlesource.com/pub.git/+/0a32ae4a folder/* should not ignore the folder itself, only the contents (#3267)
 https://dart.googlesource.com/pub.git/+/44b785aa Normalize file names for tar.gz (#3268)
 https://dart.googlesource.com/pub.git/+/2fd6b5f0 Fix repository specification: isRetracted -> retracted (#3249)
 https://dart.googlesource.com/pub.git/+/0fc71db4 Write log trace to $PUB_CACHE/log/pub_log.txt when crashing (#3240)

```

Diff: https://dart.googlesource.com/pub.git/+/dcb6abac2d7d43258c03b348be42bf4aab9529b1~..8f5ab7b1aba3b9f66b56246d77e167990339d317/
Change-Id: I54f1fde0f50ca19ca036bb1e6d9b166455031183
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/229542
Reviewed-by: Jonas Jensen <jonasfj@google.com>
Commit-Queue: Sigurd Meldgaard <sigurdm@google.com>

CHANGELOG.md

@@ -83,6 +83,17 @@ in 2018, as it doesn't work with any Dart 2.x release.
 
 [an issue]: https://github.com/dart-lang/sdk/issues/new
 
+#### Pub
+
+- Fixed race conditions in `dart pub get`, `dart run` and `dart pub global run`.
+  It should now be safe to run these concurrently.
+- If (when) Pub crashes it will save a verbose log in
+  `$PUB_CACHE/log/pub_log.txt` This can be used for filing issues to the issue
+  tracker.
+
+  `dart --verbose pub [command]` will also cause the log file to be written.
+- `dart pub add` can now add multiple packages in one command.
+
 #### Linter
 
 Updated the Linter to `1.18.0`, which includes changes that

DEPS

@@ -141,7 +141,7 @@ vars = {
   "pool_rev": "7abe634002a1ba8a0928eded086062f1307ccfae",
   "process_rev": "56ece43b53b64c63ae51ec184b76bd5360c28d0b",
   "protobuf_rev": "c1eb6cb51af39ccbaa1a8e19349546586a5c8e31",
-  "pub_rev": "dcb6abac2d7d43258c03b348be42bf4aab9529b1",
+  "pub_rev": "8f5ab7b1aba3b9f66b56246d77e167990339d317",
   "pub_semver_rev": "a43ad72fb6b7869607581b5fedcb186d1e74276a",
   "root_certificates_rev": "692f6d6488af68e0121317a9c2c9eb393eb0ee50",
   "rust_revision": "b7856f695d65a8ebc846754f97d15814bcb1c244",

pkg/dartdev/lib/dartdev.dart

@@ -128,6 +128,7 @@ class DartdevRunner extends CommandRunner<int> {
           () => analytics,
           dependencyKindCustomDimensionName: dependencyKindCustomDimensionName,
         ),
+        isVerbose: () => verbose,
       ),
     );
     addCommand(RunCommand(verbose: verbose));