Reland "Bump pub."

This is a reland of 5c9e37f
Following update of `DEPS` in `flutter/engine`:
  flutter/engine#26395

New commits include:
```
git log --format="%C(auto) %h %s" 00c00e8adf9706bebe8f94483b7663c5f36f59d2..def32ceb1d660552eaec24839d377199aea5a569
 def32ceb Revert "Revert "Use the frontend server to compile pub executables (#2968)" (#3006)" (#3008)
 0dc7e50c Make `.gitignore` and `.pubignore` case-insensitive on Windows / MacOS (#3009)
 e89d4ab8 Generate GNU-style long file names in tar archives (#3005)
 d2ad13d0 Revert "Use the frontend server to compile pub executables (#2968)" (#3006)
 492b15ba New binstubs for global activate using `dart pub` (#3002)
 e02f23bb fix grammer in .gitignore error message (#2995)
 e01e3a41 Use the frontend server to compile pub executables (#2968)
 647989c6 Use RetryClient from package:http/retry.dart (#2980)
```

Original change's description:
> Change-Id: I9a0b5fb2b5616a5a0eaa16f3a90205bb1bb1fc8f
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/200878
> Auto-Submit: Jonas Jensen <[email protected]>
> Commit-Queue: Alexander Thomas <[email protected]>
> Reviewed-by: Alexander Thomas <[email protected]>

Change-Id: I1a0570318c63ec97fd141d79b405f55105111077
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/201260
Commit-Queue: Jonas Jensen <[email protected]>
Reviewed-by: Alexander Thomas <[email protected]>

CHANGELOG.md

@@ -85,6 +85,8 @@ Updated the Linter to `1.4.0`, which includes:
   * Global ignores are no longer taken into account.
   * Even packages that are not in git source control will have their
     `.gitignore` files respected.
+  * `.gitignore` and `.pubignore` is always case-insensitive on MacOs and
+    Windows (as is default for `git` repositories).
 
 * New flag `dart pub deps --json` gives a machine parsable overview of the
   current dependencies.
@@ -100,6 +102,8 @@ Updated the Linter to `1.4.0`, which includes:
   This should fix several issues we had with incompatibilities between different
   system `tar`s.
 * `PUB_HOSTED_URL` can now include a trailing slash.
+* Incremental compilation is now used for compilation of executables from
+  dependencies when using `dart run <package>:<command>`.
 
 ### Language
 

DEPS

@@ -142,7 +142,7 @@ vars = {
   "pool_rev": "7abe634002a1ba8a0928eded086062f1307ccfae",
   "process_rev": "56ece43b53b64c63ae51ec184b76bd5360c28d0b",
   "protobuf_rev": "0d03fd588df69e9863e2a2efc0059dee8f18d5b2",
-  "pub_rev": "00c00e8adf9706bebe8f94483b7663c5f36f59d2",
+  "pub_rev": "def32ceb1d660552eaec24839d377199aea5a569",
   "pub_semver_rev": "f50d80ef10c4b2fa5f4c8878036a4d9342c0cc82",
   "resource_rev": "6b79867d0becf5395e5819a75720963b8298e9a7",
   "root_certificates_rev": "7e5ec82c99677a2e5b95ce296c4d68b0d3378ed8",