Introduce IsUndefined(Isolate*) and IsTheHole(Isolate*)

src/runtime/runtime-strings.cc

Index: src/runtime/runtime-strings.cc
diff --git a/src/runtime/runtime-strings.cc b/src/runtime/runtime-strings.cc
index 8df345313698e197ae3384456f321c989e096f86..97f21458493169d12662468161c9475869580862 100644
--- a/src/runtime/runtime-strings.cc
+++ b/src/runtime/runtime-strings.cc
@@ -725,12 +725,11 @@ static int CopyCachedOneByteCharsToArray(Heap* heap, const uint8_t* chars,
                                          FixedArray* elements, int length) {
   DisallowHeapAllocation no_gc;
   FixedArray* one_byte_cache = heap->single_character_string_cache();
-  Object* undefined = heap->undefined_value();
   int i;
   WriteBarrierMode mode = elements->GetWriteBarrierMode(no_gc);
   for (i = 0; i < length; ++i) {
     Object* value = one_byte_cache->get(chars[i]);
-    if (value == undefined) break;
+    if (value->IsUndefined(heap->isolate())) break;
     elements->set(i, value, mode);
   }
   if (i < length) {