Enable optimizer pipeline for DBC.

runtime/vm/stub_code_dbc.cc

Index: runtime/vm/stub_code_dbc.cc
diff --git a/runtime/vm/stub_code_dbc.cc b/runtime/vm/stub_code_dbc.cc
index 0f66414bcf678f32a32de4ae917521656003f352..36e44b3ce42d9a06e8719db000cd2a4e4375b0a9 100644
--- a/runtime/vm/stub_code_dbc.cc
+++ b/runtime/vm/stub_code_dbc.cc
@@ -51,6 +51,19 @@ void StubCode::GenerateMegamorphicMissStub(Assembler* assembler) {
 }
 
 
+// These deoptimization stubs are only used to populate stack frames
+// with something meaningful to make sure GC can scan the stack during
+// the last phase of deoptimization which materializes objects.
+void StubCode::GenerateDeoptimizeLazyStub(Assembler* assembler) {
+  __ Trap();
+}
+
+
+void StubCode::GenerateDeoptimizeStub(Assembler* assembler) {
+  __ Trap();
+}
+
+
 // Print the stop message.
 DEFINE_LEAF_RUNTIME_ENTRY(void, PrintStopMessage, 1, const char* message) {
   OS::Print("Stop message: %s\n", message);