Improve compilation speed on a pathological case > 2x (7 sec -> 2.7 sec) by improving local lookups.

runtime/vm/scopes.cc

 // Copyright (c) 2012, 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/scopes.h"
 
 #include "vm/ast.h"
 #include "vm/bit_vector.h"
 #include "vm/object.h"
 #include "vm/parser.h"
@@ skipping 276 matching lines @@
     SourceLabel* label = labels_[i];
     if (label->name().Equals(name)) {
       return label;
     }
   }
   return NULL;
 }
 
 
 LocalVariable* LocalScope::LocalLookupVariable(const String& name) const {
+  ASSERT(name.IsSymbol());
   for (intptr_t i = 0; i < variables_.length(); i++) {
     LocalVariable* var = variables_[i];
-    if (var->name().Equals(name) && !var->is_invisible_) {
+    ASSERT(var->name().IsSymbol());
+    if ((var->name().raw() == name.raw()) && !var->is_invisible_) {
       return var;
     }
   }
   return NULL;
 }
 
 
 LocalVariable* LocalScope::LookupVariable(const String& name, bool test_only) {
   LocalScope* current_scope = this;
   while (current_scope != NULL) {
@@ skipping 254 matching lines @@
   } else {
     // Shift negative indexes so that the lowest one is 0 (they are still
     // non-positive).
     return fixed_parameter_count -
         (index() - ParsedFunction::kFirstLocalSlotIndex);
   }
 }
 
 
 }  // namespace dart