[turbofan] Utilize the fact that empty string is canonicalized.

test/unittests/compiler/js-typed-lowering-unittest.cc

Index: test/unittests/compiler/js-typed-lowering-unittest.cc
diff --git a/test/unittests/compiler/js-typed-lowering-unittest.cc b/test/unittests/compiler/js-typed-lowering-unittest.cc
index 979d14616425fb63ceb1b935d7222421e12481aa..80e071d1ec1c696bd7434bc8da5576af8459a851 100644
--- a/test/unittests/compiler/js-typed-lowering-unittest.cc
+++ b/test/unittests/compiler/js-typed-lowering-unittest.cc
@@ -130,6 +130,17 @@ TEST_F(JSTypedLoweringTest, JSToBooleanWithReceiverOrNullOrUndefined) {
   EXPECT_THAT(r.replacement(), IsBooleanNot(IsObjectIsUndetectable(input)));
 }
 
+TEST_F(JSTypedLoweringTest, JSToBooleanWithString) {
+  Node* input = Parameter(Type::String(), 0);
+  Node* context = Parameter(Type::Any(), 1);
+  Reduction r = Reduce(graph()->NewNode(
+      javascript()->ToBoolean(ToBooleanHint::kAny), input, context));
+  ASSERT_TRUE(r.Changed());
+  EXPECT_THAT(r.replacement(),
+              IsBooleanNot(IsReferenceEqual(
+                  input, IsHeapConstant(factory()->empty_string()))));
+}
+
 TEST_F(JSTypedLoweringTest, JSToBooleanWithAny) {
   Node* input = Parameter(Type::Any(), 0);
   Node* context = Parameter(Type::Any(), 1);