Convert some compiler passes to preserve valid def-use chains.

runtime/vm/flow_graph.h

Index: runtime/vm/flow_graph.h
diff --git a/runtime/vm/flow_graph.h b/runtime/vm/flow_graph.h
index 81edee2bc754875187924f45576c15b63bcf5bde..6ba7cb17071c0770a423a22a08e9c06f262fa272 100644
--- a/runtime/vm/flow_graph.h
+++ b/runtime/vm/flow_graph.h
@@ -6,17 +6,12 @@
 #define VM_FLOW_GRAPH_H_
 
 #include "vm/growable_array.h"
+#include "vm/intermediate_language.h"
 #include "vm/parser.h"
 
 namespace dart {
 
-class BlockEntryInstr;
-class ConstantInstr;
-class Definition;
 class FlowGraphBuilder;
-class GraphEntryInstr;
-class PhiInstr;
-class ReturnInstr;
 class ValueInliningContext;
 
 class BlockIterator : public ValueObject {
@@ -117,6 +112,15 @@ class FlowGraph : public ZoneAllocated {
   ConstantInstr* AddConstantToInitialDefinitions(const Object& object);
   void AddToInitialDefinitions(Definition* defn);
 
+  void InsertBefore(Instruction* next,
+                    Instruction* instr,
+                    Environment* env,
+                    Definition::UseKind use_kind);
+  void InsertAfter(Instruction* prev,
+                   Instruction* instr,
+                   Environment* env,
+                   Definition::UseKind use_kind);
+
   // Operations on the flow graph.
   void ComputeSSA(intptr_t next_virtual_register_number,
                   GrowableArray<Definition*>* inlining_parameters);