Rework error handling in the service protocol and in Observatory.

runtime/observatory/lib/src/elements/isolate_view.dart

Index: runtime/observatory/lib/src/elements/isolate_view.dart
diff --git a/runtime/observatory/lib/src/elements/isolate_view.dart b/runtime/observatory/lib/src/elements/isolate_view.dart
index 787b1f0604bdfe712e7db2f58d192ea535135886..db65066face224a5906e25a5357a0ae77c0f22cc 100644
--- a/runtime/observatory/lib/src/elements/isolate_view.dart
+++ b/runtime/observatory/lib/src/elements/isolate_view.dart
@@ -121,29 +121,11 @@ class IsolateViewElement extends ObservatoryElement {
     }
   }
 
-  void refresh(var done) {
-    isolate.reload().whenComplete(done);
+  Future refresh() {
+    return isolate.reload();
   }
 
-  void refreshCoverage(var done) {
-    isolate.refreshCoverage().whenComplete(done);
-  }
-
-  Future pause(_) {
-    return isolate.pause().then((result) {
-        // TODO(turnidge): Instead of asserting here, handle errors
-        // properly.
-        assert(result.type == 'Success');
-        return isolate.reload();
-      });
-  }
-
-  Future resume(_) {
-    return isolate.resume().then((result) {
-        // TODO(turnidge): Instead of asserting here, handle errors
-        // properly.
-        assert(result.type == 'Success');
-        return isolate.reload();
-      });
+  Future refreshCoverage() {
+    return isolate.refreshCoverage();
   }
 }