Allocate and finalize a code object on x64 if the new compiler succeeds.

runtime/vm/flow_graph_compiler_x64.h

Index: runtime/vm/flow_graph_compiler_x64.h
diff --git a/runtime/vm/flow_graph_compiler_x64.h b/runtime/vm/flow_graph_compiler_x64.h
index db83d44811953d6f48216bb67acd8227bfb2c9d5..9e9abc6342da6f0372f1d1920d7e2a216b81b3f3 100644
--- a/runtime/vm/flow_graph_compiler_x64.h
+++ b/runtime/vm/flow_graph_compiler_x64.h
@@ -31,6 +31,11 @@ class FlowGraphCompiler : public InstructionVisitor {
 
   void CompileGraph();
 
+  // Infrastructure copied from class CodeGenerator or stubbed out.
+  void FinalizePcDescriptors(const Code& code);
+  void FinalizeVarDescriptors(const Code& code);
+  void FinalizeExceptionHandlers(const Code& code);
+
  private:
   // Bail out of the flow graph compiler.  Does not return to the caller.
   void Bailout(const char* reason);