Add font substitution metric for Linux

pdf/out_of_process_instance.cc

Index: pdf/out_of_process_instance.cc
diff --git a/pdf/out_of_process_instance.cc b/pdf/out_of_process_instance.cc
index 92511185c9715dd610adc6353cae440616666284..c2b7a2dcf6c9669cb518caf3f872a4d7980f1266 100644
--- a/pdf/out_of_process_instance.cc
+++ b/pdf/out_of_process_instance.cc
@@ -282,6 +282,7 @@ OutOfProcessInstance::OutOfProcessInstance(PP_Instance instance)
       preview_document_load_state_(LOAD_STATE_COMPLETE),
       uma_(this),
       told_browser_about_unsupported_feature_(false),
+      font_substitution_reported(false),
       print_preview_page_count_(0),
       last_progress_sent_(0),
       recently_sent_find_update_(false),
@@ -1312,6 +1313,13 @@ void OutOfProcessInstance::DocumentLoadFailed() {
   PostMessage(message);
 }
 
+void OutOfProcessInstance::FontSubstituted() {
+  if (font_substitution_reported)
+    return;
+  font_substitution_reported = true;

[rkaplow, 2016/10/05 19:40:28]

UserAction should generally be used when a user has done something explicit to
trigger it. it should be used only when we need the timestamp of the action.

Is the goal here just to count the number of times this has occured?

Also - is this meant to be a beginning step to what we discussed earlier today?

[npm, 2016/10/05 19:53:03]

I see this method being called for LoadFailure, LoadSuccess, and
PreviewDocumentLoadFailure in this same class. I believe those are not
userAction-dependent? What would be ideal here?

The goal is just to count how many times this occurs (but counting it once per
document).

This is much simpler than what we discussed today but still a useful first step.

[rkaplow, 2016/10/05 21:03:10]

Yes, it's not ideal. It is still better for it to be in a histogram since you
don't need the timing info. You can have it be a boolean histogram and just use
the 'true' bucket.

usually we like to have a baseline comparison - in this case I don't see a
natural baseline but if there is one it would be good (generally some sort of
fail case)

+  UserMetricsRecordAction("PDF.FontSubstituted");
+}
+
 void OutOfProcessInstance::PreviewDocumentLoadFailed() {
   UserMetricsRecordAction("PDF.PreviewDocumentLoadFailure");
   if (preview_document_load_state_ != LOAD_STATE_LOADING ||