Add flow graph printing into a .cfg file with flag --print-flow-graph-file.

vm/intermediate_language.h

Index: vm/intermediate_language.h
===================================================================
--- vm/intermediate_language.h	(revision 8145)
+++ vm/intermediate_language.h	(working copy)
@@ -1347,7 +1347,8 @@
   virtual type##Instr* As##type() { return this; }                             \
   virtual intptr_t InputCount() const;                                         \
   virtual const char* DebugName() const { return #type; }                      \
-  virtual void PrintTo(BufferFormatter* f) const;
+  virtual void PrintTo(BufferFormatter* f) const;                              \
+  virtual void PrintToVisualizer(BufferFormatter* f) const;
 
 
 class Instruction : public ZoneAllocated {
@@ -1381,6 +1382,12 @@
   virtual Instruction* StraightLineSuccessor() const = 0;
   virtual void SetSuccessor(Instruction* instr) = 0;
 
+  // Normal instructions can have 0 (inside a block) or 1 (last instruction in
+  // a block) successors. Branch instruction with >1 successors override this
+  // function.
+  virtual intptr_t SuccessorCount() const;
+  virtual BlockEntryInstr* SuccessorAt(intptr_t index) const;
+
   virtual void replace_computation(Computation* value) {
     UNREACHABLE();
   }
@@ -1414,6 +1421,7 @@
 
   // Printing support.
   virtual void PrintTo(BufferFormatter* f) const = 0;
+  virtual void PrintToVisualizer(BufferFormatter* f) const = 0;
 
 #define INSTRUCTION_TYPE_CHECK(type)                                           \
   virtual bool Is##type() const { return false; }                              \
@@ -1519,6 +1527,9 @@
   virtual Instruction* StraightLineSuccessor() const { return NULL; }
   virtual void SetSuccessor(Instruction* instr) { UNREACHABLE(); }
 
+  virtual intptr_t SuccessorCount() const;
+  virtual BlockEntryInstr* SuccessorAt(intptr_t index) const;
+
   virtual void DiscoverBlocks(
       BlockEntryInstr* current_block,
       GrowableArray<BlockEntryInstr*>* preorder,
@@ -1834,6 +1845,9 @@
   virtual Instruction* StraightLineSuccessor() const { return NULL; }
   virtual void SetSuccessor(Instruction* instr) { UNREACHABLE(); }
 
+  virtual intptr_t SuccessorCount() const;
+  virtual BlockEntryInstr* SuccessorAt(intptr_t index) const;
+
   virtual void DiscoverBlocks(
       BlockEntryInstr* current_block,
       GrowableArray<BlockEntryInstr*>* preorder,