Roll dart to pick up fix for diagnostic server (#4266)

* Roll dart to pick up fix for diagnostic server

* Fix runUnaryGuarded, runBinaryGuarded calls

* Revert changes to runUnaryGuarded, runBinaryGuarded as they seem to be local-only, perhaps dependent on version of analyzer

* Update third_party license hash. No changes to licenses

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': '80e3fed6df31aafa33a6a641479cb0e0031ae643',
+  'dart_revision': 'b6d7ad59dc5bb996d40726977f5798172e503bce',
 
   'dart_args_tag': '0.13.7',
   'dart_async_tag': '2.0.0',

frontend_server/test/server_test.dart

@@ -326,7 +326,7 @@ Future<int> main() async {
       final _MockedIncrementalKernelGenerator generator =
         new _MockedIncrementalKernelGenerator();
       when(generator.computeDelta()).thenReturn(new Future<DeltaProgram>.value(
-        new DeltaProgram(null /* program stub */)
+        new DeltaProgram("", null /* program stub */)
       ));
       final _MockedBinaryPrinterFactory printerFactory =
         new _MockedBinaryPrinterFactory();

travis/licenses_golden/licenses_third_party

-Signature: 9ba54648728ca2142ba5624d02a05621
+Signature: 1009ca3ead533f57956e70d0dc1e6d39
 
 UNUSED LICENSES: