Changes since last dart roll: (flutter#7316)

```
88e6fe0f67 testing: refer to issue 35508 in status file entry
bcbf47d48f [gardening] Patch flutter engine to unbreak hhh build.
4579863064 [fasta] Handle type parameters of supertypes in type arguments checks
d3a78f9c82 [gardening] Fix hot_reload_e2e_test on Windows.
8bbf240078 [infra] Explicitly pass 'debug' to pub_integration_test step from pkg_linux_debug config.
10782621d0 gitignore for generated gdb file
c10da25d48 Mark the toString method from enum declarations as being synthetic
0a0ee50501 [infra] Add debug mode support to pub_integration_test.
0b22689f21 [gardening] Mark dartfix/test/src/driver_test as RuntimeError.
```

Author: aam

DEPS

@@ -31,7 +31,7 @@ vars = {
   # Dart is: https://github.com/dart-lang/sdk/blob/master/DEPS.
   # You can use //tools/dart/create_updated_flutter_deps.py to produce
   # updated revision list of existing dependencies.
-  'dart_revision': 'd1817ddc91fd3aea061647b2e21860c47a5a5180',
+  'dart_revision': '88e6fe0f673e3d88f06fb6797103f9a9305961d9',
 
   # WARNING: DO NOT EDIT MANUALLY
   # The lines between blank lines above and below are generated by a script. See create_updated_flutter_deps.py