Parser: add usage counters for "use asm".

src/parser.h

Index: src/parser.h
diff --git a/src/parser.h b/src/parser.h
index c05b2d9cb330be6b82b6a193fe7404ff17bc6423..346f75fa2b12d12255e66c766456a79c16a58b97 100644
--- a/src/parser.h
+++ b/src/parser.h
@@ -798,6 +798,8 @@ class Parser : public ParserBase<ParserTraits> {
 
   void ThrowPendingError();
 
+  void InternalizeUseCounts();
+
   Isolate* isolate_;
 
   Handle<Script> script_;
@@ -818,6 +820,8 @@ class Parser : public ParserBase<ParserTraits> {
   const AstRawString* pending_error_arg_;
   const char* pending_error_char_arg_;
   bool pending_error_is_reference_error_;
+
+  int use_counts_[v8::Isolate::kUseCounterFeatureCount];
 };