Change how debugger handles source breakpoints

runtime/vm/json_stream.h

Index: runtime/vm/json_stream.h
===================================================================
--- runtime/vm/json_stream.h	(revision 31244)
+++ runtime/vm/json_stream.h	(working copy)
@@ -59,7 +59,7 @@
   void PrintfValue(const char* format, ...) PRINTF_ATTRIBUTE(2, 3);
   void PrintValue(const Object& o, bool ref = true);
   void PrintValue(const Field& f, const Instance& instance, bool ref = true);
-  void PrintValue(const SourceBreakpoint* bpt);
+  void PrintValue(SourceBreakpoint* bpt);
 
   void PrintPropertyBool(const char* name, bool b);
   void PrintProperty(const char* name, intptr_t i);
@@ -158,7 +158,7 @@
                 bool ref = true) const {
     stream_->PrintValue(field, instance, ref);
   }
-  void AddValue(const SourceBreakpoint* bpt) const {
+  void AddValue(SourceBreakpoint* bpt) const {
     stream_->PrintValue(bpt);
   }
   void AddValueF(const char* format, ...) const PRINTF_ATTRIBUTE(2, 3);