Minor JSON cleanup. Also added comment requested for r8086.

src/runtime.cc

 // Copyright 2011 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 5084 matching lines @@
   *(write_cursor++) = '"';
   return new_string;
 }
 
 
 template <typename SinkChar, typename SourceChar>
 static inline SinkChar* WriteQuoteJsonString(
     Isolate* isolate,
     SinkChar* write_cursor,
     Vector<const SourceChar> characters) {
+  // SinkChar is only char if SourceChar is guaranteed to be char.
+  ASSERT(sizeof(SinkChar) >= sizeof(SourceChar));
   const SourceChar* read_cursor = characters.start();
   const SourceChar* end = read_cursor + characters.length();
   *(write_cursor++) = '"';
   while (read_cursor < end) {
     SourceChar c = *(read_cursor++);
     if (sizeof(SourceChar) > 1u &&
         static_cast<unsigned>(c) >= kQuoteTableLength) {
       *(write_cursor++) = static_cast<SinkChar>(c);
     } else {
       int len = JsonQuoteLengths[static_cast<unsigned>(c)];
@@ skipping 7208 matching lines @@
   } else {
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(false);
   }
 }
 
 
 } }  // namespace v8::internal