Rework error handling in the service protocol and in Observatory.

runtime/observatory/tests/service/native_metrics_test.dart

Index: runtime/observatory/tests/service/native_metrics_test.dart
diff --git a/runtime/observatory/tests/service/native_metrics_test.dart b/runtime/observatory/tests/service/native_metrics_test.dart
index 8a8e11aaad888bb0c3fabae28764fd5843617aed..0a84204d43b732817458fc377569ecb58c436639 100644
--- a/runtime/observatory/tests/service/native_metrics_test.dart
+++ b/runtime/observatory/tests/service/native_metrics_test.dart
@@ -17,29 +17,38 @@ void script() {
 
 var tests = [
 
-(Isolate isolate) =>
-    isolate.refreshNativeMetrics().then((Map metrics) {
-      expect(metrics.length, greaterThan(1));
-      expect(metrics.length, greaterThan(1));
-      var foundOldHeapCapacity = metrics.values.any((m) =>
-          m.name == 'heap.old.capacity');
-      expect(foundOldHeapCapacity, equals(true));
-  }),
-
-(Isolate isolate) =>
-  isolate.invokeRpc('getIsolateMetric',
-                    { 'metricId': 'metrics/native/heap.old.used' })
-      .then((ServiceMetric counter) {
+  (Isolate isolate) async {
+    Map metrics = await isolate.refreshNativeMetrics();
+    expect(metrics.length, greaterThan(1));
+    expect(metrics.length, greaterThan(1));
+    var foundOldHeapCapacity = metrics.values.any(
+        (m) => m.name == 'heap.old.capacity');
+    expect(foundOldHeapCapacity, equals(true));
+  },
+
+  (Isolate isolate) async {
+    var params = { 'metricId': 'metrics/native/heap.old.used' };
+    ServiceMetric counter =
+      await isolate.invokeRpc('getIsolateMetric', params);
     expect(counter.type, equals('Counter'));
     expect(counter.name, equals('heap.old.used'));
-  }),
-
-(Isolate isolate) =>
-    isolate.invokeRpc('getIsolateMetric',
-                      { 'metricId': 'metrics/native/doesnotexist' })
-          .then((DartError err) {
-    expect(err is DartError, isTrue);
-  }),
+  },
+
+  (Isolate isolate) async {
+    bool caughtException;
+    try {
+      await isolate.invokeRpc('getIsolateMetric',
+                              { 'metricId': 'metrics/native/doesnotexist' });
+      expect(false, isTrue, reason:'Unreachable');
+    } on ServerRpcException catch (e) {
+      caughtException = true;
+      expect(e.code, equals(ServerRpcException.kInvalidParams));
+      expect(e.message,
+             "getIsolateMetric: invalid 'metricId' "
+             "parameter: metrics/native/doesnotexist");
+    }
+    expect(caughtException, isTrue);
+  },
 
 ];