Mark null and undefined as undetectable, and use it to handle abstract equality comparison in the g…

src/crankshaft/mips/lithium-codegen-mips.cc

Index: src/crankshaft/mips/lithium-codegen-mips.cc
diff --git a/src/crankshaft/mips/lithium-codegen-mips.cc b/src/crankshaft/mips/lithium-codegen-mips.cc
index dc3d62df90f2cec797be2595be7378a8f492b6c4..ad23b1c721463936ec691f5c0e587e92d39912ff 100644
--- a/src/crankshaft/mips/lithium-codegen-mips.cc
+++ b/src/crankshaft/mips/lithium-codegen-mips.cc
@@ -5252,8 +5252,8 @@ Condition LCodeGen::EmitTypeofIs(Label* true_label,
     final_branch_condition = eq;
 
   } else if (String::Equals(type_name, factory->undefined_string())) {
-    __ LoadRoot(at, Heap::kUndefinedValueRootIndex);
-    __ Branch(USE_DELAY_SLOT, true_label, eq, at, Operand(input));
+    __ LoadRoot(at, Heap::kNullValueRootIndex);
+    __ Branch(USE_DELAY_SLOT, false_label, eq, at, Operand(input));
     // The first instruction of JumpIfSmi is an And - it is safe in the delay
     // slot.
     __ JumpIfSmi(input, false_label);