[es6] implement destructuring assignment

src/crankshaft/hydrogen.cc

Index: src/crankshaft/hydrogen.cc
diff --git a/src/crankshaft/hydrogen.cc b/src/crankshaft/hydrogen.cc
index e80c6aecede77aa0e04a4b468ea42792b2d6b459..7312ac5cd1e06e7d0a4695129aa2333a14f36c41 100644
--- a/src/crankshaft/hydrogen.cc
+++ b/src/crankshaft/hydrogen.cc
@@ -7039,6 +7039,7 @@ void HOptimizedGraphBuilder::VisitAssignment(Assignment* expr) {
   DCHECK(!HasStackOverflow());
   DCHECK(current_block() != NULL);
   DCHECK(current_block()->HasPredecessor());
+
   VariableProxy* proxy = expr->target()->AsVariableProxy();
   Property* prop = expr->target()->AsProperty();
   DCHECK(proxy == NULL || prop == NULL);
@@ -12133,6 +12134,12 @@ void HOptimizedGraphBuilder::VisitExportDeclaration(
 }
 
 
+void HOptimizedGraphBuilder::VisitRewritableAssignmentExpression(
+    RewritableAssignmentExpression* node) {
+  CHECK_ALIVE(Visit(node->expression()));
+}
+
+
 // Generators for inline runtime functions.
 // Support for types.
 void HOptimizedGraphBuilder::GenerateIsSmi(CallRuntime* call) {