Ensure we do not clobber the register holding the elements backing store.

test/mjsunit/regress/regress-crbug-162085.js

Index: test/mjsunit/regress/regress-crbug-162085.js
diff --git a/test/mjsunit/regress/regress-crbug-162085.js b/test/mjsunit/regress/regress-crbug-162085.js
index f26c711f7ad5bbafc36dcfc4e719c95b64737027..a53b2c9987f47a953ff78c166592ba33aecc40fc 100644
--- a/test/mjsunit/regress/regress-crbug-162085.js
+++ b/test/mjsunit/regress/regress-crbug-162085.js
@@ -30,6 +30,7 @@
 var a = [1,2,3];
 a.length = 0;
 a[0] = 1.4;
+assertEquals(1.4, a[0]);
 assertEquals(undefined, a[1]);
 assertEquals(undefined, a[2]);
 assertEquals(undefined, a[3]);
@@ -43,6 +44,7 @@ var a2 = [1.3];
 grow_store(a2,1,1.4);
 a2.length = 0;
 grow_store(a2,0,1.5);
+assertEquals(1.5, a2[0]);
 assertEquals(undefined, a2[1]);
 assertEquals(undefined, a2[2]);
 assertEquals(undefined, a2[3]);
@@ -53,3 +55,17 @@ var o = {};
 grow_store(a3, 1, o);
 assertEquals(1.3, a3[0]);
 assertEquals(o, a3[1]);
+
+// Ensure the double array growstub initializes the array with holes.
+function grow_store2(a,i,v) {
+  a[i] = v;
+}
+
+var a4 = [1.3];
+grow_store2(a4,1,1.4);
+a4.length = 0;
+grow_store2(a4,0,1);
+assertEquals(1, a4[0]);
+assertEquals(undefined, a4[1]);
+assertEquals(undefined, a4[2]);
+assertEquals(undefined, a4[3]);