Clean up is-ASCII checks.

src/heap-inl.h

 // Copyright 2006-2010 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 25 matching lines @@
 namespace internal {
 
 int Heap::MaxObjectSizeInPagedSpace() {
   return Page::kMaxHeapObjectSize;
 }
 
 
 MaybeObject* Heap::AllocateStringFromUtf8(Vector<const char> str,
                                           PretenureFlag pretenure) {
   // Check for ASCII first since this is the common case.
-  for (int i = 0; i < str.length(); ++i) {
-    if (static_cast<uint8_t>(str[i]) > String::kMaxAsciiCharCodeU) {
-      // Non-ASCII and we need to decode.
-      return AllocateStringFromUtf8Slow(str, pretenure);
-    }
+  if (String::IsAscii(str.start(), str.length())) {
+    // If the string is ASCII, we do not need to convert the characters
+    // since UTF8 is backwards compatible with ASCII.
+    return AllocateStringFromAscii(str, pretenure);
   }
-  // If the string is ASCII, we do not need to convert the characters
-  // since UTF8 is backwards compatible with ASCII.
-  return AllocateStringFromAscii(str, pretenure);
+  // Non-ASCII and we need to decode.
+  return AllocateStringFromUtf8Slow(str, pretenure);
 }
 
 
 MaybeObject* Heap::AllocateSymbol(Vector<const char> str,
                                   int chars,
                                   uint32_t hash_field) {
   unibrow::Utf8InputBuffer<> buffer(str.start(),
                                     static_cast<unsigned>(str.length()));
   return AllocateInternalSymbol(&buffer, chars, hash_field);
 }
@@ skipping 450 matching lines @@
 
 
 void ExternalStringTable::ShrinkNewStrings(int position) {
   new_space_strings_.Rewind(position);
   Verify();
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_INL_H_