[turbofan] add ForTesting to pipeline entry points that are for testing only.

test/cctest/compiler/test-codegen-deopt.cc

Index: test/cctest/compiler/test-codegen-deopt.cc
diff --git a/test/cctest/compiler/test-codegen-deopt.cc b/test/cctest/compiler/test-codegen-deopt.cc
index 3b68470a62fc16dac9e6bce119711a79d0446bcb..56afe7b6dd399df2049bbc43f3dbbb17c63cba65 100644
--- a/test/cctest/compiler/test-codegen-deopt.cc
+++ b/test/cctest/compiler/test-codegen-deopt.cc
@@ -63,12 +63,7 @@ class DeoptCodegenTester {
     if (FLAG_trace_turbo) {
       os << *schedule;
     }
-
-    Linkage* linkage = new (scope_->main_zone()) Linkage(info.zone(), &info);
-    Pipeline pipeline(&info);
-    result_code =
-        pipeline.GenerateCodeForMachineGraph(linkage, graph, schedule);
-
+    result_code = Pipeline::GenerateCodeForTesting(&info, graph, schedule);
 #ifdef OBJECT_PRINT
     if (FLAG_print_opt_code || FLAG_trace_turbo) {
       result_code->Print();