Move ReturnInstr to new scheme (x64 and ia32) and implement more code in new ia32 compiler.

runtime/vm/flow_graph_compiler_x64.h

Index: runtime/vm/flow_graph_compiler_x64.h
===================================================================
--- runtime/vm/flow_graph_compiler_x64.h	(revision 8165)
+++ runtime/vm/flow_graph_compiler_x64.h	(working copy)
@@ -50,11 +50,17 @@
                       Register reg1,
                       Register reg2);
 
+  bool is_optimizing() const { return is_optimizing_; }
+  const ParsedFunction& parsed_function() const { return parsed_function_; }
 
   void GenerateCallRuntime(intptr_t cid,
                            intptr_t token_index,
                            intptr_t try_index,
                            const RuntimeEntry& entry);
+  void AddCurrentDescriptor(PcDescriptors::Kind kind,
+                            intptr_t cid,
+                            intptr_t token_index,
+                            intptr_t try_index);
 
   // Returns true if the next block after current in the current block order
   // is the given block.
@@ -93,8 +99,6 @@
 
   BlockEntryInstr* current_block() const { return current_block_; }
 
-  bool is_optimizing() const { return is_optimizing_; }
-
   // Bail out of the flow graph compiler.  Does not return to the caller.
   void Bailout(const char* reason);
 
@@ -142,10 +146,6 @@
                     intptr_t try_index,
                     const ExternalLabel* label,
                     PcDescriptors::Kind kind);
-  void AddCurrentDescriptor(PcDescriptors::Kind kind,
-                            intptr_t cid,
-                            intptr_t token_index,
-                            intptr_t try_index);
 
   // Type checking helper methods.
   void CheckClassIds(const GrowableArray<intptr_t>& class_ids,