dart2js: get:hashCode methods to avoid Object.hashCode

pkg/compiler/lib/src/elements/modelx.dart

Index: pkg/compiler/lib/src/elements/modelx.dart
diff --git a/pkg/compiler/lib/src/elements/modelx.dart b/pkg/compiler/lib/src/elements/modelx.dart
index d832c07f9b10054efdc313f5c77ede1b6f3ef844..a087bcf01593acb1bc18c5e65357b44e21d6467d 100644
--- a/pkg/compiler/lib/src/elements/modelx.dart
+++ b/pkg/compiler/lib/src/elements/modelx.dart
@@ -39,12 +39,14 @@ import 'visitor.dart' show ElementVisitor;
 abstract class DeclarationSite {}
 
 abstract class ElementX extends Element with ElementCommon {
-  static int elementHashCode = 0;
+  static int _elementHashCode = 0;
+  static int newHashCode() =>
+      _elementHashCode = (_elementHashCode + 1).toUnsigned(30);
 
   final String name;
   final ElementKind kind;
   final Element enclosingElement;
-  final int hashCode = ++elementHashCode;
+  final int hashCode = newHashCode();
   List<MetadataAnnotation> metadataInternal;
 
   ElementX(this.name, this.kind, this.enclosingElement) {
@@ -3186,6 +3188,8 @@ class JumpTargetX implements JumpTarget {
   bool isBreakTarget = false;
   bool isContinueTarget = false;
 
+  final int hashCode = ElementX.newHashCode();
+
   JumpTargetX(this.statement, this.nestingLevel, this.executableContext);
 
   String get name => "target";
@@ -3285,6 +3289,8 @@ abstract class MetadataAnnotationX implements MetadataAnnotation {
 
   Token get endToken;
 
+  final int hashCode = ElementX.newHashCode();
+
   MetadataAnnotationX([this.resolutionState = STATE_NOT_STARTED]);
 
   MetadataAnnotation ensureResolved(Resolution resolution) {