Move invalid string length check to the factory.

src/factory.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_FACTORY_H_
 #define V8_FACTORY_H_
 
 #include "src/isolate.h"
 
 namespace v8 {
@@ skipping 104 matching lines @@
         STATIC_ASCII_VECTOR(str), pretenure).ToHandleChecked();
   }
 
   inline Handle<String> NewStringFromAsciiChecked(
       const char* str,
       PretenureFlag pretenure = NOT_TENURED) {
     return NewStringFromOneByte(
         OneByteVector(str), pretenure).ToHandleChecked();
   }
 
+
+  // Allocates and fully initializes a String.  There are two String
+  // encodings: ASCII and two byte. One should choose between the three string
+  // allocation functions based on the encoding of the string buffer used to
+  // initialized the string.
+  //   - ...FromAscii initializes the string from a buffer that is ASCII
+  //     encoded (it does not check that the buffer is ASCII encoded) and the
+  //     result will be ASCII encoded.
+  //   - ...FromUTF8 initializes the string from a buffer that is UTF-8
+  //     encoded.  If the characters are all single-byte characters, the
+  //     result will be ASCII encoded, otherwise it will converted to two
+  //     byte.
+  //   - ...FromTwoByte initializes the string from a buffer that is two-byte
+  //     encoded.  If the characters are all single-byte characters, the
+  //     result will be converted to ASCII, otherwise it will be left as
+  //     two-byte.
+
   // TODO(dcarney): remove this function.
   MUST_USE_RESULT inline MaybeHandle<String> NewStringFromAscii(
       Vector<const char> str,
       PretenureFlag pretenure = NOT_TENURED) {
     return NewStringFromOneByte(Vector<const uint8_t>::cast(str), pretenure);
   }
 
   // UTF8 strings are pretenured when used for regexp literal patterns and
   // flags in the parser.
   MUST_USE_RESULT MaybeHandle<String> NewStringFromUtf8(
@@ skipping 560 matching lines @@
                                  PretenureFlag pretenure = TENURED);
 
   Handle<JSFunction> NewFunction(Handle<Map> map,
                                  Handle<String> name,
                                  MaybeHandle<Code> maybe_code);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_FACTORY_H_