Add property reflection for Polymer computed property and complex obs…

…erver strings

Closes #3184.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=232359838

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

@@ -56,6 +56,9 @@ final class CheckSideEffects extends AbstractPostOrderCallback
 
   private final boolean protectSideEffectFreeCode;
 
+  /** Whether the synthetic extern for JSCOMPILER_PRESERVE has been injected */
+  private boolean preserveFunctionInjected = false;
+
   CheckSideEffects(AbstractCompiler compiler, boolean report,
       boolean protectSideEffectFreeCode) {
     this.compiler = compiler;
@@ -170,7 +173,9 @@ public void visit(NodeTraversal t, Node n, Node parent) {
    */
   private void protectSideEffects() {
     if (!problemNodes.isEmpty()) {
-      addExtern();
+      if (!preserveFunctionInjected) {
+        addExtern(compiler);
+      }
       for (Node n : problemNodes) {
         Node name = IR.name(PROTECTOR_FN).srcref(n);
         name.putBooleanProp(Node.IS_CONSTANT_NAME, true);
@@ -183,7 +188,8 @@ private void protectSideEffects() {
     }
   }
 
-  private void addExtern() {
+  /** Injects JSCOMPILER_PRESEVE into the synthetic externs */
+  static void addExtern(AbstractCompiler compiler) {
     Node name = IR.name(PROTECTOR_FN);
     name.putBooleanProp(Node.IS_CONSTANT_NAME, true);
     Node var = IR.var(name);
@@ -245,6 +251,10 @@ public void visit(NodeTraversal t, Node n, Node parent) {
           noSideEffectExterns.add(name);
         }
       }
+
+      if (n.isName() && PROTECTOR_FN.equals(n.getString())) {
+        preserveFunctionInjected = true;
+      }
     }
   }
 }

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

@@ -340,7 +340,9 @@ public boolean isPropertyTestFunction(Node call) {
 
   @Override
   public boolean isPropertyRenameFunction(String name) {
-    return super.isPropertyRenameFunction(name) || "goog.reflect.objectProperty".equals(name);
+    return super.isPropertyRenameFunction(name)
+        || "goog.reflect.objectProperty".equals(name)
+        || "$jscomp.reflectProperty".equals(name);
   }
 
   @Override