Fixes change tracking in StripCode.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=152965110

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

@@ -277,7 +277,10 @@ LifeCycleStage getLifeCycleStage() {
   /** True iff a function changed since the last time a pass was run */
   abstract boolean hasScopeChanged(Node n);
 
-  /** Passes that do cross-scope modifications use this (eg, InlineVariables) */
+  /**
+   * Passes that make modifications in a scope that is different than the Compiler.currentScope use
+   * this (eg, InlineVariables and many others)
+   */
   abstract void reportChangeToEnclosingScope(Node n);
 
   /**

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

@@ -2377,6 +2377,17 @@ void setScope(Node n) {
   }
 
   private Node getEnclosingChangeScope(Node n) {
+    /**
+     * Compiler change reporting usually occurs after the AST change has already occurred. In the
+     * case of node removals those nodes are already removed from the tree and so have no parent
+     * chain to walk. In these situations changes are reported instead against what (used to be)
+     * their parent. If that parent is itself a script node then it's important to be able to
+     * recognize it as the enclosing scope without first stepping to its parent as well.
+     */
+    if (n.isScript()) {
+      return n;
+    }
+
     while (n.getParent() != null) {
       n = n.getParent();
       if (n.isFunction() || n.isScript()) {

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

@@ -4758,7 +4758,7 @@ public void visit(Node n) {
               } else {
                 Preconditions.checkState(
                     isEquivalentToExcludingFunctions(n, clone),
-                    "%schange scope not marked as changed",
+                    "%schanged scope not marked as changed",
                     passNameMsg);
               }
             }

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

@@ -261,31 +261,34 @@ void maybeRemoveReferenceToRemovedVariable(NodeTraversal t, Node n,
     void replaceHighestNestedCallWithNull(Node node, Node parent) {
       Node ancestor = parent;
       Node ancestorChild = node;
+      Node ancestorParent;
       while (true) {
+        ancestorParent = ancestor.getParent();
+
         if (ancestor.getFirstChild() != ancestorChild) {
           replaceWithNull(ancestorChild, ancestor);
           break;
         }
         if (ancestor.isExprResult()) {
           // Remove the entire expression statement.
-          Node ancParent = ancestor.getParent();
-          replaceWithEmpty(ancestor, ancParent);
+          replaceWithEmpty(ancestor, ancestorParent);
           break;
         }
         if (ancestor.isAssign()) {
-          Node ancParent = ancestor.getParent();
-          ancParent.replaceChild(ancestor, ancestor.getLastChild().detach());
+          ancestorParent.replaceChild(ancestor, ancestor.getLastChild().detach());
           break;
         }
         if (!NodeUtil.isGet(ancestor)
             && !ancestor.isCall()) {
           replaceWithNull(ancestorChild, ancestor);
           break;
         }
+
+        // Is not executed on the last iteration so can't be used for change reporting.
         ancestorChild = ancestor;
-        ancestor = ancestor.getParent();
+        ancestor = ancestorParent;
       }
-      compiler.reportCodeChange();
+      compiler.reportChangeToEnclosingScope(ancestorParent);
     }
 
     /**
@@ -312,7 +315,7 @@ void maybeEliminateAssignmentByLvalueName(NodeTraversal t, Node n,
         if (parent.isExprResult()) {
           Node grandparent = parent.getParent();
           replaceWithEmpty(parent, grandparent);
-          compiler.reportCodeChange();
+          compiler.reportChangeToEnclosingScope(grandparent);
         } else {
           t.report(n, STRIP_ASSIGNMENT_ERROR, lvalue.getQualifiedName());
         }
@@ -341,10 +344,11 @@ void maybeEliminateExpressionByName(NodeTraversal t, Node n,
         if (parent.isExprResult()) {
           Node grandparent = parent.getParent();
           replaceWithEmpty(parent, grandparent);
+          compiler.reportChangeToEnclosingScope(grandparent);
         } else {
           replaceWithEmpty(n, parent);
+          compiler.reportChangeToEnclosingScope(parent);
         }
-        compiler.reportCodeChange();
       }
     }
 
@@ -384,7 +388,7 @@ void eliminateKeysWithStripNamesFromObjLit(NodeTraversal t, Node n) {
           Node next = key.getNext();
           n.removeChild(key);
           key = next;
-          compiler.reportCodeChange();
+          compiler.reportChangeToEnclosingScope(n);
         } else {
           key = key.getNext();
         }

test/com/google/javascript/jscomp/StripCodeTest.java

@@ -31,12 +31,6 @@ public StripCodeTest() {
     super(EXTERNS, true);
   }
 
-  @Override
-  protected void setUp() throws Exception {
-    super.setUp();
-    validateAstChangeMarking(false);
-  }
-
   /**
    * Creates an instance for removing logging code.
    *
@@ -71,7 +65,8 @@ private static StripCode createLoggerInstance(Compiler compiler) {
         stripNamePrefixes);
   }
 
-  @Override public CompilerPass getProcessor(Compiler compiler) {
+  @Override
+  public CompilerPass getProcessor(Compiler compiler) {
     return createLoggerInstance(compiler);
   }