[debugger] add lcov support to d8.

src/d8.h

Index: src/d8.h
diff --git a/src/d8.h b/src/d8.h
index bedf43ef6671fadc02dec46fd5cce19f549528f6..c4e33fc6455ac0ae68c946cdcfb9072d1abceaee 100644
--- a/src/d8.h
+++ b/src/d8.h
@@ -304,7 +304,8 @@ class ShellOptions {
         natives_blob(NULL),
         snapshot_blob(NULL),
         trace_enabled(false),
-        trace_config(NULL) {}
+        trace_config(NULL),
+        lcov_file(NULL) {}
 
   ~ShellOptions() {
     delete[] isolate_sources;
@@ -335,6 +336,7 @@ class ShellOptions {
   const char* snapshot_blob;
   bool trace_enabled;
   const char* trace_config;
+  const char* lcov_file;
 };
 
 class Shell : public i::AllStatic {
@@ -464,6 +466,8 @@ class Shell : public i::AllStatic {
   static std::vector<ExternalizedContents> externalized_contents_;
 
   static void WriteIgnitionDispatchCountersFile(v8::Isolate* isolate);
+  // Append LCOV coverage data to file.
+  static void WriteLcovData(v8::Isolate* isolate, const char* file);
   static Counter* GetCounter(const char* name, bool is_histogram);
   static Local<String> Stringify(Isolate* isolate, Local<Value> value);
   static void Initialize(Isolate* isolate);