Add breakpoints and single-stepping to Observatory.

runtime/vm/json_stream.cc

Index: runtime/vm/json_stream.cc
diff --git a/runtime/vm/json_stream.cc b/runtime/vm/json_stream.cc
index 2726c8a38fbef922ebe45c4b76ed57d36d504344..d72ff5bd765090a135348fd253d7c6b2b676e414 100644
--- a/runtime/vm/json_stream.cc
+++ b/runtime/vm/json_stream.cc
@@ -307,6 +307,12 @@ void JSONStream::PrintProperty(const char* name, const DebuggerEvent* event) {
 }
 
 
+void JSONStream::PrintProperty(const char* name, SourceBreakpoint* bpt) {
+  PrintPropertyName(name);
+  PrintValue(bpt);
+}
+
+
 void JSONStream::PrintProperty(const char* name, Isolate* isolate) {
   PrintPropertyName(name);
   PrintValue(isolate);