[debug] use best effort coverage when enabling precise coverage.

src/debug/debug-coverage.cc

Index: src/debug/debug-coverage.cc
diff --git a/src/debug/debug-coverage.cc b/src/debug/debug-coverage.cc
index 06f2ad466fbba85ddb67bc75caf077871aa4654f..eae8d1c99845bd80f9373c82e47c4ce670d1add3 100644
--- a/src/debug/debug-coverage.cc
+++ b/src/debug/debug-coverage.cc
@@ -140,7 +140,6 @@ void Coverage::TogglePrecise(Isolate* isolate, bool enable) {
         FeedbackVector* vector = FeedbackVector::cast(current_obj);
         SharedFunctionInfo* shared = vector->shared_function_info();
         if (!shared->IsSubjectToDebugging()) continue;
-        vector->clear_invocation_count();
         vectors.emplace_back(vector, isolate);
       }
     }
@@ -149,13 +148,6 @@ void Coverage::TogglePrecise(Isolate* isolate, bool enable) {
         ArrayList::New(isolate, static_cast<int>(vectors.size()));
     for (const auto& vector : vectors) list = ArrayList::Add(list, vector);
     isolate->SetCodeCoverageList(*list);
-    // Increment count for functions currently on the stack. We won't observe
-    // entry of these functions, but we know they have coverage.
-    for (JavaScriptFrameIterator it(isolate); !it.done(); it.Advance()) {
-      JSFunction* function = it.frame()->function();
-      if (!function->shared()->IsSubjectToDebugging()) continue;
-      function->feedback_vector()->increment_invocation_count();
-    }
   } else {
     isolate->SetCodeCoverageList(isolate->heap()->undefined_value());
   }