[debug] refactor code coverage to use enum for mode.

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index cc62391ecc10f2549d7f2c62c379df0eadf8b28c..c9aaa2b6f0d4a5cdf7f3272236e6a86a54ad8478 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -2539,7 +2539,9 @@ int Shell::RunMain(Isolate* isolate, int argc, char* argv[], bool last_run) {
     options.isolate_sources[i].StartExecuteInThread();
   }
   {
-    if (options.lcov_file) debug::Coverage::TogglePrecise(isolate, true);
+    if (options.lcov_file) {
+      debug::Coverage::SelectMode(isolate, debug::Coverage::kPreciseCount);
+    }
     HandleScope scope(isolate);
     Local<Context> context = CreateEvaluationContext(isolate);
     if (last_run && options.use_interactive_shell()) {