[Interpreter] Optimize equality check with null/undefined with a check on the map.

test/cctest/interpreter/bytecode_expectations/Generators.golden

Index: test/cctest/interpreter/bytecode_expectations/Generators.golden
diff --git a/test/cctest/interpreter/bytecode_expectations/Generators.golden b/test/cctest/interpreter/bytecode_expectations/Generators.golden
index 1f379c0306f2b81b27be6bfba767821aeaba0778..a576b910d9c2180bf09f79d4a49e23c3113b7d7c 100644
--- a/test/cctest/interpreter/bytecode_expectations/Generators.golden
+++ b/test/cctest/interpreter/bytecode_expectations/Generators.golden
@@ -277,7 +277,7 @@ snippet: "
 "
 frame size: 17
 parameter count: 1
-bytecode array length: 771
+bytecode array length: 769
 bytecodes: [
                 B(Ldar), R(new_target),
                 B(JumpIfUndefined), U8(28),
@@ -475,9 +475,8 @@ bytecodes: [
                 B(StaContextSlot), R(1), U8(11), U8(0),
                 B(LdaContextSlot), R(1), U8(11), U8(0),
                 B(Star), R(10),
-                B(LdaNull),
-                B(TestEqual), R(10), U8(18),
-                B(JumpIfFalse), U8(4),
+                B(TestUndetectable), R(10),
+                B(JumpIfToBooleanFalse), U8(4),

[rmcilroy, 2016/12/05 10:57:19]

Could you add an explicit BytecodeGeneratorTest for this logic please?

[mythria, 2016/12/05 14:53:11]

Done.

                 B(JumpConstant), U8(16),
                 B(LdaContextSlot), R(1), U8(9), U8(0),
                 B(Star), R(10),
@@ -620,13 +619,13 @@ constant pool: [
   ONE_BYTE_INTERNALIZED_STRING_TYPE [""],
   FIXED_ARRAY_TYPE,
   Smi [133],
-  Smi [161],
-  Smi [581],
+  Smi [159],
+  Smi [579],
 ]
 handlers: [
-  [46, 690, 696],
+  [46, 688, 694],
   [143, 438, 444],
   [146, 394, 396],
-  [542, 558, 560],
+  [540, 556, 558],
 ]