Rename DartMetadata in preparation for supporting real metadata

compiler/java/com/google/dart/compiler/ast/DartDeclaration.java

Index: compiler/java/com/google/dart/compiler/ast/DartDeclaration.java
===================================================================
--- compiler/java/com/google/dart/compiler/ast/DartDeclaration.java	(revision 10855)
+++ compiler/java/com/google/dart/compiler/ast/DartDeclaration.java	(working copy)
@@ -14,7 +14,7 @@
 
   private N name; // Not visited.
   private DartComment dartDoc;
-  private DartMetadata metadata = DartMetadata.EMPTY;
+  private DartObsoleteMetadata metadata = DartObsoleteMetadata.EMPTY;
 
   protected DartDeclaration(N name) {
     this.name = becomeParentOf(name);
@@ -37,11 +37,11 @@
     this.dartDoc = dartDoc;
   }
 
-  public DartMetadata getMetadata() {
+  public DartObsoleteMetadata getMetadata() {
     return metadata;
   }
 
-  public void setMetadata(DartMetadata metadata) {
+  public void setMetadata(DartObsoleteMetadata metadata) {
     this.metadata = metadata;
   }