Use fast path for sliced and external strings in ConvertCase.

test/mjsunit/string-case.js

 // Copyright 2008 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
 //       with the distribution.
 //     * Neither the name of Google Inc. nor the names of its
 //       contributors may be used to endorse or promote products derived
 //       from this software without specific prior written permission.
 //
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-// Flags: --random-seed=17
+// Flags: --random-seed=17 --allow-natives-syntax
+// Flags: --expose-externalize-string
 
 assertEquals("ΚΟΣΜΟΣ ΚΟΣΜΟΣ".toLowerCase(), "κοσμος κοσμος");
 
 var A_CODE = "A".charCodeAt(0);
 var Z_CODE = "Z".charCodeAt(0);
 var a_CODE = "a".charCodeAt(0);
 var z_CODE = "z".charCodeAt(0);
 
 function charCodeToLower(charCode) {
   if (A_CODE <= charCode && charCode <= Z_CODE) {
@@ skipping 12 matching lines @@
 function test(length) {
   var str = "";
   var strLower = "";
   var strUpper = "";
   for (var i = 0; i < length; i++) {
     var c = Math.round(0x7f * Math.random());
     str += String.fromCharCode(c);
     strLower += String.fromCharCode(charCodeToLower(c));
     strUpper += String.fromCharCode(charCodeToUpper(c));
   }
+  %FlattenString(strLower);
+  %FlattenString(strUpper);
+  // Sequential string.
+  assertEquals(strLower, str.toLowerCase());
+  assertEquals(strUpper, str.toUpperCase());
+  // Cons string.
+  assertEquals(strLower + strLower, (str + str).toLowerCase());
+  assertEquals(strUpper + strUpper, (str + str).toUpperCase());
+  // Sliced string.
+  assertEquals(strLower.substring(1), str.substring(1).toLowerCase());
+  assertEquals(strUpper.substring(1), str.substring(1).toUpperCase());
+  // External string.
+  externalizeString(str, false);
   assertEquals(strLower, str.toLowerCase());
   assertEquals(strUpper, str.toUpperCase());
 }
 
 for (var i = 1; i <= 128; i <<= 1); {
   for (var j = 0; j < 8; j++) {
     for (var k = 0; k < 3; k++) {
       test(i + j);
     }
   }
 }