Reduce the runtime of the DeadPropertyAssignmentEliminationPass.

Only process functions that have changed since the last time the pass ran.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=134430398

src/com/google/javascript/jscomp/DeadPropertyAssignmentElimination.java

@@ -21,19 +21,17 @@
 import com.google.common.collect.Iterators;
 import com.google.common.collect.PeekingIterator;
 import com.google.common.collect.Sets;
-import com.google.javascript.jscomp.NodeTraversal.AbstractPostOrderCallback;
 import com.google.javascript.jscomp.NodeTraversal.Callback;
+import com.google.javascript.jscomp.NodeTraversal.FunctionCallback;
 import com.google.javascript.rhino.Node;
 import com.google.javascript.rhino.Token;
-
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.LinkedList;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Queue;
 import java.util.Set;
-
 import javax.annotation.Nullable;
 
 /**
@@ -83,25 +81,23 @@ public void process(Node externs, Node root) {
 
     Set<String> blacklistedPropNames = Sets.union(
         getterSetterCollector.propNames, compiler.getExternProperties());
-    NodeTraversal.traverseEs6(compiler, root, new FunctionVisitor(compiler, blacklistedPropNames));
-  }
 
-  private static class FunctionVisitor extends AbstractPostOrderCallback {
+    NodeTraversal.traverseChangedFunctions(compiler, new FunctionVisitor(blacklistedPropNames));
+  }
 
-    private final AbstractCompiler compiler;
+  private static class FunctionVisitor implements FunctionCallback {
 
     /**
      * A set of properties names that are potentially unsafe to remove duplicate writes to.
      */
     private final Set<String> blacklistedPropNames;
 
-    FunctionVisitor(AbstractCompiler compiler, Set<String> blacklistedPropNames) {
-      this.compiler = compiler;
+    FunctionVisitor(Set<String> blacklistedPropNames) {
       this.blacklistedPropNames = blacklistedPropNames;
     }
 
     @Override
-    public void visit(NodeTraversal t, Node n, Node parent) {
+    public void enterFunction(AbstractCompiler compiler, Node n) {
       if (!n.isFunction()) {
         return;
       }