Use getLhsNodesOfDeclaration instead of just iterating through the pa…

…ram list.

This avoids a crash when a param is something other than just a name, such as DEFAULT_VALUE node.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=170752700

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

@@ -363,8 +363,8 @@ private void traverseNode(Node n, Node parent, Scope scope) {
               && "arguments".equals(n.getString())
               && var.equals(scope.getArgumentsVar())) {
             Scope fnScope = var.getScope();
-            Node lp = fnScope.getRootNode().getSecondChild();
-            for (Node p = lp.getFirstChild(); p != null; p = p.getNext()) {
+            Node paramList = NodeUtil.getFunctionParameters(fnScope.getRootNode());
+            for (Node p : NodeUtil.getLhsNodesOfDeclaration(paramList)) {
               Var paramVar = fnScope.getOwnSlot(p.getString());
               checkNotNull(paramVar);
               markReferencedVar(paramVar);

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

@@ -305,8 +305,7 @@ public void testDefaultParamsInClass() {
         "class Foo extends Bar { constructor(value = undefined) { super(); value; } }; new Foo;");
   }
 
-  // TODO(tbreisacher): Fix and enable.
-  public void disabled_testDefaultParamsInClassThatReferencesArguments() {
+  public void testDefaultParamsInClassThatReferencesArguments() {
     testSame(
         LINE_JOINER.join(
             "class Foo extends Bar {",