Revert "Give instances their own model class; move DartErrors out of instance-ref into their own er…

runtime/bin/vmservice/observatory/lib/src/elements/observatory_element.dart

Index: runtime/bin/vmservice/observatory/lib/src/elements/observatory_element.dart
diff --git a/runtime/bin/vmservice/observatory/lib/src/elements/observatory_element.dart b/runtime/bin/vmservice/observatory/lib/src/elements/observatory_element.dart
index 4dccf987b54d039ec03ae8d79fb81c3e221dd8fc..86012aef1a0b15316ac1283ad6c2d68b3ea65e7e 100644
--- a/runtime/bin/vmservice/observatory/lib/src/elements/observatory_element.dart
+++ b/runtime/bin/vmservice/observatory/lib/src/elements/observatory_element.dart
@@ -111,4 +111,64 @@ class ObservatoryElement extends PolymerElement {
   }
 
   int parseInt(String value) => int.parse(value);
+
+  bool isNull(ref) {
+    return ref != null && ref.serviceType == 'Null';
+  }
+
+  bool isSentinel(ref) {
+    return ref != null && ref.serviceType == 'Sentinel';
+  }
+
+  bool isError(ref) {
+    return ref != null && ref.serviceType == 'Error';
+  }
+
+  bool isInt(ref) {
+    return ref != null && (ref.serviceType == 'Smi' ||
+                           ref.serviceType == 'Mint' ||
+                           ref.serviceType == 'Bigint');
+  }
+
+  bool isBool(ref) {
+    return ref != null && ref.serviceType == 'Bool';
+  }
+
+  bool isString(ref) {
+    return ref != null && ref.serviceType == 'String';
+  }
+
+  bool isInstance(ref) {
+    return ref != null && ref.serviceType == 'Instance';
+  }
+
+  bool isDouble(ref) {
+    return ref != null && ref.serviceType == 'Double';
+  }
+
+  bool isList(ref) {
+    return ref != null && (ref.serviceType == 'GrowableObjectArray' ||
+            ref.serviceType == 'Array');
+  }
+
+  bool isType(ref) {
+    return ref != null && (ref.serviceType == 'Type');
+  }
+
+  bool isUnexpected(ref) {
+    if (ref == null) return false;
+    return (!['Null',
+              'Sentinel',
+              'Smi',
+              'Mint',
+              'Bigint',
+              'Bool',
+              'String',
+              'Double',
+              'Instance',
+              'GrowableObjectArray',
+              'Array',
+              'Type',
+              'Error'].contains(ref.serviceType));
+  }
 }