Add source fingerprint computation to function. Will be used to detect unexpected changes of functi…

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 15166)
+++ runtime/vm/object.h	(working copy)
@@ -1433,6 +1433,10 @@
                                          const Function& parent,
                                          intptr_t token_pos);
 
+  // Slow function, use in asserts to track changes in important library
+  // functions.
+  intptr_t SourceFingerprint() const;
+
   static const int kCtorPhaseInit = 1 << 0;
   static const int kCtorPhaseBody = 1 << 1;
   static const int kCtorPhaseAll = (kCtorPhaseInit | kCtorPhaseBody);