Fix warnings on Win64.

src/scanner.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 42 matching lines @@
   void Reset() {
     if (data_ == NULL) {
       data_ = NewArray<char>(kInitialCapacity);
       limit_ = ComputeLimit(data_, kInitialCapacity);
     }
     cursor_ = data_;
   }
 
   int pos() const {
     ASSERT_NOT_NULL(data_);
-    return cursor_ - data_;
+    return static_cast<int>(cursor_ - data_);
   }
 
   char* data() const { return data_; }
 
  private:
   static const int kInitialCapacity = 256;
   char* data_;
   char* cursor_;
   char* limit_;
 
   int Capacity() const {
     ASSERT_NOT_NULL(data_);
-    return (limit_ - data_) + unibrow::Utf8::kMaxEncodedSize;
+    return static_cast<int>(limit_ - data_) + unibrow::Utf8::kMaxEncodedSize;
   }
 
   static char* ComputeLimit(char* data, int capacity) {
     return (data + capacity) - unibrow::Utf8::kMaxEncodedSize;
   }
 
   void AddCharSlow(uc32 c);
 };
 
 
@@ skipping 329 matching lines @@
   }
 
   // Decodes a unicode escape-sequence which is part of an identifier.
   // If the escape sequence cannot be decoded the result is kBadRune.
   uc32 ScanIdentifierUnicodeEscape();
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_SCANNER_H_