[debugger] add precise mode for code coverage.

src/runtime/runtime-debug.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/compiler.h"
 #include "src/debug/debug-coverage.h"
 #include "src/debug/debug-evaluate.h"
@@ skipping 1917 matching lines @@
     JSObject::AddProperty(script_obj, id_string,
                           factory->NewNumberFromInt(script.script_id), NONE);
     JSObject::AddProperty(
         script_obj, entries_string,
         factory->NewJSArrayWithElements(entries_array, FAST_ELEMENTS), NONE);
     scripts_array->set(i, *script_obj);
   }
   return *factory->NewJSArrayWithElements(scripts_array, FAST_ELEMENTS);
 }
 
+RUNTIME_FUNCTION(Runtime_DebugTogglePreciseCoverage) {
+  SealHandleScope shs(isolate);
+  CONVERT_BOOLEAN_ARG_CHECKED(enable, 0);
+  if (enable) {
+    Coverage::EnablePrecise(isolate);
+  } else {
+    Coverage::DisablePrecise(isolate);
+  }
+  return isolate->heap()->undefined_value();
+}
+
 }  // namespace internal
 }  // namespace v8