VM: Add infrastructure to support deferred generation of unoptimized code.

runtime/vm/stub_code_mips.cc

Index: runtime/vm/stub_code_mips.cc
===================================================================
--- runtime/vm/stub_code_mips.cc	(revision 44707)
+++ runtime/vm/stub_code_mips.cc	(working copy)
@@ -588,7 +588,8 @@
   // Frame is fully rewritten at this point and it is safe to perform a GC.
   // Materialize any objects that were deferred by FillFrame because they
   // require allocation.
-  __ EnterStubFrame();
+  // Enter stub frame with loading PP. The caller's PP is not materialized yet.
+  __ EnterStubFrame(true);
   if (preserve_result) {
     __ Push(T1);  // Preserve result, it will be GC-d here.
   }