Statically check for assignments to const in harmony mode.

src/ast.cc

Index: src/ast.cc
diff --git a/src/ast.cc b/src/ast.cc
index 13e55894d58cb0560e3fcd39b89edb1735420652..577b0ef53a02f1c90335b535f3de7a4e870a578c 100644
--- a/src/ast.cc
+++ b/src/ast.cc
@@ -70,6 +70,7 @@ VariableProxy::VariableProxy(Isolate* isolate, Variable* var)
       var_(NULL),  // Will be set by the call to BindTo.
       is_this_(var->is_this()),
       is_trivial_(false),
+      is_used_as_lvalue_(false),
       position_(RelocInfo::kNoPosition) {
   BindTo(var);
 }
@@ -84,6 +85,7 @@ VariableProxy::VariableProxy(Isolate* isolate,
       var_(NULL),
       is_this_(is_this),
       is_trivial_(false),
+      is_used_as_lvalue_(false),
       position_(position) {
   // Names must be canonicalized for fast equality checks.
   ASSERT(name->IsSymbol());