Added BlockFrequencyInfo::view for displaying the block frequency propagation graph via graphviz.

This is useful for debugging issues in the BlockFrequency implementation since
one can easily visualize where probability mass and other errors occur in the
propagation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194654 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/BlockFrequencyInfo.h

@@ -41,6 +41,8 @@ public:
 
   bool runOnFunction(Function &F);
   void print(raw_ostream &O, const Module *M) const;
+  const Function *getFunction() const;
+  void view() const;
 
   /// getblockFreq - Return block frequency. Return 0 if we don't have the
   /// information. Please note that initial frequency is equal to ENTRY_FREQ. It