Generate some intrinsics using our IR.

runtime/vm/flow_graph_allocator.h

Index: runtime/vm/flow_graph_allocator.h
===================================================================
--- runtime/vm/flow_graph_allocator.h	(revision 39651)
+++ runtime/vm/flow_graph_allocator.h	(working copy)
@@ -56,7 +56,8 @@
   // Number of stack slots needed for a fpu register spill slot.
   static const intptr_t kDoubleSpillFactor = kDoubleSize / kWordSize;
 
-  explicit FlowGraphAllocator(const FlowGraph& flow_graph);
+  explicit FlowGraphAllocator(const FlowGraph& flow_graph,
+                              bool intrinsics_mode = false);
 
   void AllocateRegisters();
 
@@ -324,6 +325,8 @@
 
   intptr_t cpu_spill_slot_count_;
 
+  bool intrinsic_mode_;
+
   DISALLOW_COPY_AND_ASSIGN(FlowGraphAllocator);
 };