Give instances their own model class; move DartErrors out of instance-ref into their own error-ref.

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 86012aef1a0b15316ac1283ad6c2d68b3ea65e7e..4dccf987b54d039ec03ae8d79fb81c3e221dd8fc 100644
--- a/runtime/bin/vmservice/observatory/lib/src/elements/observatory_element.dart
+++ b/runtime/bin/vmservice/observatory/lib/src/elements/observatory_element.dart
@@ -111,64 +111,4 @@ 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));
-  }
 }