Convert sliced strings into sequential strings when promoting into old space.

test/mjsunit/string-slices.js

Index: test/mjsunit/string-slices.js
diff --git a/test/mjsunit/string-slices.js b/test/mjsunit/string-slices.js
index b0b05eca366b3a490be84b32c088b6a14aa7e11e..cbc763d551e0ae9ebc1038bb7c4e07ac1126a901 100755
--- a/test/mjsunit/string-slices.js
+++ b/test/mjsunit/string-slices.js
@@ -25,7 +25,7 @@
 // (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: --string-slices --expose-externalize-string
+// Flags: --string-slices --expose-externalize-string --expose-gc
 
 var s = 'abcdefghijklmn';
 assertEquals(s, s.substr());
@@ -113,7 +113,6 @@ var cache = [];
 for (var i = 0; i < 10000; i++) {
   var z = x.substring(i % xl);
   assertEquals(xl - (i % xl), z.length);
-  cache.push(z);
 }
 
 
@@ -132,7 +131,6 @@ var cache = [];
 for (var i = 0; i < 10000; i++) {
   var z = x.substring(i % xl);
   assertEquals(xl - (i % xl), z.length);
-  cache.push(z);
 }
 
 // Substring of substring.
@@ -145,6 +143,14 @@ for (var i = 0; i < 64; i++) {
   cache.push(z);
   offset += i;
 }
+
+// Fill up new space with junk and then invoke GC.
+var fill = [];
+for (var i = 0; i < 100000; i++) {
+  fill.push(i + " ");
+}
+gc(true);
+
 for (var i = 63; i >= 0; i--) {
   var z = cache.pop();
   assertTrue(/\u2028123456789ABCDEF/.test(z));