Group lexical context variables for faster look up.

src/runtime/runtime-scopes.cc

Index: src/runtime/runtime-scopes.cc
diff --git a/src/runtime/runtime-scopes.cc b/src/runtime/runtime-scopes.cc
index ff7e783393081cbe731a8d5f265a5b0fa852b773..06f84598438dc0e56761499823696dd8ee962269 100644
--- a/src/runtime/runtime-scopes.cc
+++ b/src/runtime/runtime-scopes.cc
@@ -36,9 +36,7 @@ static Object* DeclareGlobals(Isolate* isolate, Handle<GlobalObject> global,
                               bool is_const, bool is_function) {
   Handle<ScriptContextTable> script_contexts(
       global->native_context()->script_context_table());
-  ScriptContextTable::LookupResult lookup;
-  if (ScriptContextTable::Lookup(script_contexts, name, &lookup) &&
-      IsLexicalVariableMode(lookup.mode)) {
+  if (ScriptContextTable::LookupLexical(script_contexts, name)) {
     return ThrowRedeclarationError(isolate, name);
   }
 
@@ -624,9 +622,13 @@ static Object* FindNameClash(Handle<ScopeInfo> scope_info,
   for (int var = 0; var < scope_info->ContextLocalCount(); var++) {
     Handle<String> name(scope_info->ContextLocalName(var));
     VariableMode mode = scope_info->ContextLocalMode(var);
-    ScriptContextTable::LookupResult lookup;
-    if (ScriptContextTable::Lookup(script_context, name, &lookup)) {
-      if (IsLexicalVariableMode(mode) || IsLexicalVariableMode(lookup.mode)) {
+    if (IsLexicalVariableMode(mode)) {
+      ScriptContextTable::LookupResult lookup;
+      if (ScriptContextTable::Lookup(script_context, name, &lookup)) {
+        return ThrowRedeclarationError(isolate, name);
+      }
+    } else {
+      if (ScriptContextTable::LookupLexical(script_context, name)) {
         return ThrowRedeclarationError(isolate, name);
       }
     }