JS tree shaking for incremental builds.

compiler/java/com/google/dart/compiler/backend/js/analysis/DependencyComputer.java

Index: compiler/java/com/google/dart/compiler/backend/js/analysis/DependencyComputer.java
diff --git a/compiler/java/com/google/dart/compiler/backend/js/analysis/DependencyComputer.java b/compiler/java/com/google/dart/compiler/backend/js/analysis/DependencyComputer.java
index 52884d714f7d833b11eb338642b98b3b61704234..3a35d219a6cc8e7033fe44179ec691af17cdb6b8 100644
--- a/compiler/java/com/google/dart/compiler/backend/js/analysis/DependencyComputer.java
+++ b/compiler/java/com/google/dart/compiler/backend/js/analysis/DependencyComputer.java
@@ -64,16 +64,22 @@ class DependencyComputer {
 
           /*
            * Whenever we see an instantiation we must check it and any super type for members that
-           * match the virtual names seen to date. 
+           * match the virtual names seen to date and we must ensure that the corresponding inherits
+           * get emitted. 
            */
           while (instantiatedClass != null) {
+            JavascriptElement inheritsInvocation = instantiatedClass.getInheritsInvocation();
+            if (inheritsInvocation != null) {
+              dependencies.add(inheritsInvocation);
+            }
+            
             for (JavascriptElement member : instantiatedClass.getMembers()) {
               if (virtualNames.contains(member.getName())) {
                 dependencies.add(member);
               }
             }
             
-            instantiatedClass = instantiatedClass.getInherits();
+            instantiatedClass = instantiatedClass.getInheritsElement();
           }
         }
       }