Run dartfmt on all files under runtime.

runtime/observatory/tests/observatory_ui/mocks/repositories/retained_size.dart

Index: runtime/observatory/tests/observatory_ui/mocks/repositories/retained_size.dart
diff --git a/runtime/observatory/tests/observatory_ui/mocks/repositories/retained_size.dart b/runtime/observatory/tests/observatory_ui/mocks/repositories/retained_size.dart
index 9f56299a6dadda4382940c0dc4712a5e2fe2843c..d5dba6fedd5c74db6e321f4e9dc782cedc8a8eeb 100644
--- a/runtime/observatory/tests/observatory_ui/mocks/repositories/retained_size.dart
+++ b/runtime/observatory/tests/observatory_ui/mocks/repositories/retained_size.dart
@@ -4,8 +4,8 @@
 
 part of mocks;
 
-typedef Future<M.Guarded<M.Instance>>
-        RetainedSizeRepositoryMockGetter(M.IsolateRef i, String id);
+typedef Future<M.Guarded<M.Instance>> RetainedSizeRepositoryMockGetter(
+    M.IsolateRef i, String id);
 
 class RetainedSizeRepositoryMock implements M.RetainedSizeRepository {
   final RetainedSizeRepositoryMockGetter _getter;
@@ -15,10 +15,9 @@ class RetainedSizeRepositoryMock implements M.RetainedSizeRepository {
       return _getter(i, id);
     }
     return new Future.value(
-      new GuardedMock<M.Instance>.fromSentinel(new SentinelMock())
-    );
+        new GuardedMock<M.Instance>.fromSentinel(new SentinelMock()));
   }
 
   RetainedSizeRepositoryMock({RetainedSizeRepositoryMockGetter getter})
-    : _getter = getter;
+      : _getter = getter;
 }