Fix crashing bug due to the fact that external one byte strings cannot be escaped

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 4925 matching lines @@
     return &raw_ptr(str)->data_[index];
   }
 
   static RawOneByteString* ReadFrom(SnapshotReader* reader,
                                     intptr_t object_id,
                                     intptr_t tags,
                                     Snapshot::Kind kind);
 
   friend class Class;
   friend class String;
+  friend class ExternalOneByteString;
   friend class SnapshotReader;
 };
 
 
 class TwoByteString : public AllStatic {
  public:
   static int32_t CharAt(const String& str, intptr_t index) {
     return *CharAddr(str, index);
   }
 
@@ skipping 101 matching lines @@
   static RawExternalOneByteString* New(const uint8_t* characters,
                                        intptr_t len,
                                        void* peer,
                                        Dart_PeerFinalizer callback,
                                        Heap::Space space);
 
   static RawExternalOneByteString* null() {
     return reinterpret_cast<RawExternalOneByteString*>(Object::null());
   }
 
+  static RawOneByteString* EscapeSpecialCharacters(const String& str);
+
   static const ClassId kClassId = kExternalOneByteStringCid;
 
  private:
   static RawExternalOneByteString* raw(const String& str) {
     return reinterpret_cast<RawExternalOneByteString*>(str.raw());
   }
 
   static RawExternalOneByteString* raw_ptr(const String& str) {
     return reinterpret_cast<RawExternalOneByteString*>(str.raw_ptr());
   }
@@ skipping 1135 matching lines @@
 
 
 RawObject* MegamorphicCache::GetTargetFunction(const Array& array,
                                                intptr_t index) {
   return array.At((index * kEntryLength) + kTargetFunctionIndex);
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_