Only add API-triggered compilation to compile-script histogram.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 8ddd351f9e32067f14a6edffe5076f177a6924d9..9b6be9ac556bee65c45f635b9dcba90028d5c9e3 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -1598,6 +1598,7 @@ Local<UnboundScript> ScriptCompiler::CompileUnbound(
   ENTER_V8(isolate);
   i::SharedFunctionInfo* raw_result = NULL;
   { i::HandleScope scope(isolate);
+    i::HistogramTimerScope total(isolate->counters()->compile_script(), true);
     i::Handle<i::Object> name_obj;
     int line_offset = 0;
     int column_offset = 0;