[debugger] add lcov support to d8.

src/debug/debug-coverage.h

 // Copyright 2017 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.
 
 #ifndef V8_DEBUG_DEBUG_COVERAGE_H_
 #define V8_DEBUG_DEBUG_COVERAGE_H_
 
 #include <vector>
 
 #include "src/allocation.h"
@@ skipping 18 matching lines @@
   };
 
   struct ScriptData {
     // Initialize top-level function in case it has been garbage-collected.
     ScriptData(Handle<Script> s, int source_length)
         : script(s), toplevel(0, source_length, 1) {}
     Handle<Script> script;
     Range toplevel;
   };
 
-  static std::vector<ScriptData> Collect(Isolate* isolate);
+  V8_EXPORT_PRIVATE static std::vector<ScriptData> Collect(Isolate* isolate);
 
   // Enable precise code coverage. This disables optimization and makes sure
   // invocation count is not affected by GC.
-  static void EnablePrecise(Isolate* isolate);
-  static void DisablePrecise(Isolate* isolate);
+  V8_EXPORT_PRIVATE static void EnablePrecise(Isolate* isolate);
+  V8_EXPORT_PRIVATE static void DisablePrecise(Isolate* isolate);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_DEBUG_DEBUG_COVERAGE_H_