Improve performance of String.fromCharCodes by implementing it in Dart. Add tow internal natives to…

runtime/vm/object.h

 // 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.
 
 #ifndef VM_OBJECT_H_
 #define VM_OBJECT_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/utils.h"
@@ skipping 4404 matching lines @@
   friend class ExternalTwoByteString;
 };
 
 
 class OneByteString : public AllStatic {
  public:
   static int32_t CharAt(const String& str, intptr_t index) {
     return *CharAddr(str, index);
   }
 
+  static void SetCharAt(const String& str, intptr_t index, uint8_t code_point) {
+    *CharAddr(str, index) = code_point;
+  }
   static RawOneByteString* EscapeSpecialCharacters(const String& str);
 
   // We use the same maximum elements for all strings.
   static const intptr_t kBytesPerElement = 1;
   static const intptr_t kMaxElements = String::kMaxElements;
 
   static intptr_t data_offset() { return OFFSET_OF(RawOneByteString, data_); }
 
   static intptr_t InstanceSize() {
     ASSERT(sizeof(RawOneByteString) == OFFSET_OF(RawOneByteString, data_));
@@ skipping 1288 matching lines @@
 
 
 RawObject* MegamorphicCache::GetTargetFunction(const Array& array,
                                                intptr_t index) {
   return array.At((index * kEntryLength) + kTargetFunctionIndex);
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_