HasOnlyAsciiChars can return incorrect results. Fixup usages and rename.

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 2c11f047dc2d8e2b58dc88425d117faf973108db..08378f195525fc4c3272f72356547dc360a3f823 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -355,14 +355,14 @@ bool String::IsTwoByteRepresentationUnderneath() {
 }
 
 
-bool String::HasOnlyAsciiChars() {
+bool String::HasOnlyOneByteChars() {
   uint32_t type = map()->instance_type();
-  return (type & kAsciiDataHintMask) == kAsciiDataHintTag;
+  return (type & kOneByteDataHintMask) == kOneByteDataHintTag;
 }
 
 
 bool String::IsOneByteConvertible() {
-  return HasOnlyAsciiChars() || IsOneByteRepresentation();
+  return HasOnlyOneByteChars() || IsOneByteRepresentation();
 }