Fix 'typeof null' canonicalization in crankshaft

src/crankshaft/hydrogen-instructions.cc

Index: src/crankshaft/hydrogen-instructions.cc
diff --git a/src/crankshaft/hydrogen-instructions.cc b/src/crankshaft/hydrogen-instructions.cc
index 3d48d8fb71862d1e486ac6f0cc68911a8759f8a0..cc1009d3a138c2aaa39b780a96764e68289170bf 100644
--- a/src/crankshaft/hydrogen-instructions.cc
+++ b/src/crankshaft/hydrogen-instructions.cc
@@ -1203,6 +1203,10 @@ namespace {
 String* TypeOfString(HConstant* constant, Isolate* isolate) {
   Heap* heap = isolate->heap();
   if (constant->HasNumberValue()) return heap->number_string();
+  if (constant->GetInstanceType() == ODDBALL_TYPE &&
+      constant->GetUnique().IsKnownGlobal(heap->null_value())) {
+    return heap->object_string();
+  }
   if (constant->IsUndetectable()) return heap->undefined_string();
   if (constant->HasStringValue()) return heap->string_string();
   switch (constant->GetInstanceType()) {