[debugger] only track LiveEdit if source changes.

src/runtime/runtime-liveedit.cc

Index: src/runtime/runtime-liveedit.cc
diff --git a/src/runtime/runtime-liveedit.cc b/src/runtime/runtime-liveedit.cc
index 5f2cac4938c0e0d2cb991b69729ef8f1217885ff..dd3405a44cd811f74f1d7ac61a80ceef4a0979b4 100644
--- a/src/runtime/runtime-liveedit.cc
+++ b/src/runtime/runtime-liveedit.cc
@@ -229,9 +229,14 @@ RUNTIME_FUNCTION(Runtime_LiveEditCompareStrings) {
   CONVERT_ARG_HANDLE_CHECKED(String, s1, 0);
   CONVERT_ARG_HANDLE_CHECKED(String, s2, 1);
 
-  isolate->debug()->feature_tracker()->Track(DebugFeatureTracker::kLiveEdit);
+  Handle<JSArray> result = LiveEdit::CompareStrings(s1, s2);
+  uint32_t array_length;
+  CHECK(result->length()->ToArrayLength(&array_length));
+  if (array_length > 0) {
+    isolate->debug()->feature_tracker()->Track(DebugFeatureTracker::kLiveEdit);
+  }
 
-  return *LiveEdit::CompareStrings(s1, s2);
+  return *result;
 }