Fix temp variable allocation in await transformation

runtime/vm/ast_transformer.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/ast_transformer.h"
 
 #include "vm/object_store.h"
 #include "vm/parser.h"
 #include "vm/thread.h"
 
@@ skipping 48 matching lines @@
   return result_;
 }
 
 
 LocalVariable* AwaitTransformer::EnsureCurrentTempVar() {
   const char* await_temp_prefix = ":await_temp_var_";
   const String& cnt_str = String::ZoneHandle(
       Z, String::NewFormatted("%s%d", await_temp_prefix, temp_cnt_));
   const String& symbol = String::ZoneHandle(Z, Symbols::New(cnt_str));
   ASSERT(!symbol.IsNull());
-  // Look up the variable through the preamble scope.
-  LocalVariable* await_tmp = preamble_->scope()->LookupVariable(symbol, false);
+  // Look up the variable in the scope used for async temp variables.
+  LocalVariable* await_tmp = function_top_->LocalLookupVariable(symbol);
   if (await_tmp == NULL) {
-    // If we need a new temp variable, we add it to the function's top scope.
+    // We need a new temp variable; add it to the function's top scope.
     await_tmp = new (Z) LocalVariable(
         Scanner::kNoSourcePos, symbol, Type::ZoneHandle(Type::DynamicType()));
     function_top_->AddVariable(await_tmp);
     // After adding it to the top scope, we can look it up from the preamble.
     // The following call includes an ASSERT check.
     await_tmp = GetVariableInScope(preamble_->scope(), symbol);
   }
   return await_tmp;
 }
 
@@ skipping 539 matching lines @@
 
 
 void AwaitTransformer::VisitThrowNode(ThrowNode* node) {
   AstNode* new_exception = Transform(node->exception());
   result_ = new(Z) ThrowNode(node->token_pos(),
                              new_exception,
                              node->stacktrace());
 }
 
 }  // namespace dart