Fixes a couple problems with GC of unoptimized code.

runtime/vm/flow_graph_compiler_ia32.cc

Index: runtime/vm/flow_graph_compiler_ia32.cc
===================================================================
--- runtime/vm/flow_graph_compiler_ia32.cc	(revision 30197)
+++ runtime/vm/flow_graph_compiler_ia32.cc	(working copy)
@@ -64,12 +64,12 @@
   // The real frame starts here.
   builder->MarkFrameStart();
 
-  // Callee's PC marker is not used anymore. Pass Function::null() to set to 0.
-  builder->AddPcMarker(Function::Handle(), slot_ix++);
+  // Callee's PC marker is not used anymore. Pass Code::null() to set to 0.
+  builder->AddPcMarker(Code::Handle(), slot_ix++);
 
   // Current FP and PC.
   builder->AddCallerFp(slot_ix++);
-  builder->AddReturnAddress(current->function(), deopt_id(), slot_ix++);
+  builder->AddReturnAddress(current->code(), deopt_id(), slot_ix++);
 
   // Emit all values that are needed for materialization as a part of the
   // expression stack for the bottom-most frame. This guarantees that GC
@@ -84,7 +84,7 @@
   }
 
   // Current PC marker and caller FP.
-  builder->AddPcMarker(current->function(), slot_ix++);
+  builder->AddPcMarker(current->code(), slot_ix++);
   builder->AddCallerFp(slot_ix++);
 
   Environment* previous = current;
@@ -92,7 +92,7 @@
   while (current != NULL) {
     // For any outer environment the deopt id is that of the call instruction
     // which is recorded in the outer environment.
-    builder->AddReturnAddress(current->function(),
+    builder->AddReturnAddress(current->code(),
                               Isolate::ToDeoptAfter(current->deopt_id()),
                               slot_ix++);
 
@@ -114,7 +114,7 @@
     }
 
     // PC marker and caller FP.
-    builder->AddPcMarker(current->function(), slot_ix++);
+    builder->AddPcMarker(current->code(), slot_ix++);
     builder->AddCallerFp(slot_ix++);
 
     // Iterate on the outer environment.