Mark script kinds as private in the service protocol.

runtime/vm/debugger_test.cc

Index: runtime/vm/debugger_test.cc
diff --git a/runtime/vm/debugger_test.cc b/runtime/vm/debugger_test.cc
index 8b537d76d8e09e0e0fd170ed4fc29b56fbf787c6..72eff9e05d96673a1d52ba78cd3a5ed5f8199a72 100644
--- a/runtime/vm/debugger_test.cc
+++ b/runtime/vm/debugger_test.cc
@@ -75,14 +75,14 @@ TEST_CASE(Debugger_PrintBreakpointsToJSONArray) {
         "\"script\":{\"type\":\"@Script\",\"fixedId\":true,"
         "\"id\":\"libraries\\/%" Pd "\\/scripts\\/test-lib\","
         "\"uri\":\"test-lib\","
-        "\"kind\":\"script\"},\"tokenPos\":14}},"
+        "\"_kind\":\"script\"},\"tokenPos\":14}},"
         "{\"type\":\"Breakpoint\",\"fixedId\":true,\"id\":\"breakpoints\\/1\","
         "\"breakpointNumber\":1,\"resolved\":false,"
         "\"location\":{\"type\":\"Location\","
         "\"script\":{\"type\":\"@Script\",\"fixedId\":true,"
         "\"id\":\"libraries\\/%" Pd "\\/scripts\\/test-lib\","
         "\"uri\":\"test-lib\","
-        "\"kind\":\"script\"},\"tokenPos\":5}}]",
+        "\"_kind\":\"script\"},\"tokenPos\":5}}]",
         vmlib.index(), vmlib.index());
   }
 }