Address comments on double-parse implementation from earlier CL.

runtime/vm/object.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/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 16909 matching lines @@
   // TODO(cshapiro): create a fast-path for OneByteString instances.
   return Transform(CaseMapping::ToLower, str, space);
 }
 
 bool String::ParseDouble(const String& str,
                          intptr_t start, intptr_t end,
                          double* result) {
   ASSERT(0 <= start);
   ASSERT(start <= end);
   ASSERT(end <= str.Length());
-  int length = end - start;
+  intptr_t length = end - start;
   NoGCScope no_gc;
   const uint8_t* startChar;
   if (str.IsOneByteString()) {
     startChar = OneByteString::CharAddr(str, start);
   } else if (str.IsExternalOneByteString()) {
     startChar = ExternalOneByteString::CharAddr(str, start);
   } else {
     uint8_t* chars = Isolate::Current()->current_zone()->Alloc<uint8_t>(length);
-    for (int i = 0; i < length; i++) {
-      int ch = str.CharAt(start + i);
+    const Scanner::CharAtFunc char_at = str.CharAtFunc();
+    for (intptr_t i = 0; i < length; i++) {
+      int32_t ch = char_at(str, start + i);
       if (ch < 128) {
         chars[i] = ch;
       } else {
         return false;  // Not ASCII, so definitely not valid double numeral.
       }
     }
     startChar = chars;
   }
   return CStringToDouble(reinterpret_cast<const char*>(startChar),
                          length, result);
@@ skipping 2084 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart