[turbofan] Improve typed lowering rules for JSToBoolean.

test/unittests/compiler/graph-unittest.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "test/unittests/compiler/graph-unittest.h"
 
 #include "src/compiler/node-properties.h"
 #include "src/factory.h"
 #include "src/objects-inl.h"  // TODO(everyone): Make typer.h IWYU compliant.
 #include "test/unittests/compiler/node-test-utils.h"
@@ skipping 80 matching lines @@
 
 Matcher<Node*> GraphTest::IsFalseConstant() {
   return IsHeapConstant(factory()->false_value());
 }
 
 
 Matcher<Node*> GraphTest::IsTrueConstant() {
   return IsHeapConstant(factory()->true_value());
 }
 
+Matcher<Node*> GraphTest::IsNullConstant() {
+  return IsHeapConstant(factory()->null_value());
+}
 
 Matcher<Node*> GraphTest::IsUndefinedConstant() {
   return IsHeapConstant(factory()->undefined_value());
 }
 
 TypedGraphTest::TypedGraphTest(int num_parameters)
     : GraphTest(num_parameters), typer_(isolate(), Typer::kNoFlags, graph()) {}
 
 TypedGraphTest::~TypedGraphTest() {}
 
@@ skipping 20 matching lines @@
   EXPECT_LT(0u, n0->id());
   EXPECT_LT(0u, n1->id());
   EXPECT_NE(n0->id(), n1->id());
   EXPECT_EQ(&kDummyOperator, n0->op());
   EXPECT_EQ(&kDummyOperator, n1->op());
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8