Add metrics to printer setup flow.

chrome/browser/ui/webui/settings/chromeos/cups_printers_handler.cc

Index: chrome/browser/ui/webui/settings/chromeos/cups_printers_handler.cc
diff --git a/chrome/browser/ui/webui/settings/chromeos/cups_printers_handler.cc b/chrome/browser/ui/webui/settings/chromeos/cups_printers_handler.cc
index fbf676442a9a98b6841a8d26419119ab3155f849..af1b541f28e3d84a4eb1fd6c874b1c9e42ddcd88 100644
--- a/chrome/browser/ui/webui/settings/chromeos/cups_printers_handler.cc
+++ b/chrome/browser/ui/webui/settings/chromeos/cups_printers_handler.cc
@@ -11,6 +11,7 @@
 #include "base/files/file_util.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/memory/ptr_util.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/path_service.h"
 #include "base/strings/string_util.h"
 #include "base/threading/sequenced_task_runner_handle.h"
@@ -44,6 +45,14 @@ namespace settings {
 
 namespace {
 
+// These values are written to logs.  New enum values can be added, but existing
+// enums must never be renumbered or deleted and reused.
+enum PpdSourceForHistogram { kUser = 0, kScs = 1, kPpdSourceMax };
+
+void RecordPpdSource(const PpdSourceForHistogram& source) {
+  UMA_HISTOGRAM_ENUMERATION("Printing.CUPS.PpdSource", kUser, kPpdSourceMax);
+}
+
 void OnRemovedPrinter(bool success) {}
 
 std::unique_ptr<base::DictionaryValue> GetPrinterInfo(const Printer& printer) {
@@ -225,6 +234,7 @@ void CupsPrintersHandler::HandleAddCupsPrinter(const base::ListValue* args) {
 
   // Verify a valid ppd path is present.
   if (!printer_ppd_path.empty()) {
+    RecordPpdSource(kUser);
     GURL tmp = net::FilePathToFileURL(base::FilePath(printer_ppd_path));
     if (!tmp.is_valid()) {
       LOG(ERROR) << "Invalid ppd path: " << printer_ppd_path;
@@ -233,6 +243,7 @@ void CupsPrintersHandler::HandleAddCupsPrinter(const base::ListValue* args) {
     }
     printer->mutable_ppd_reference()->user_supplied_ppd_url = tmp.spec();
   } else if (!printer_manufacturer.empty() && !printer_model.empty()) {
+    RecordPpdSource(kScs);
     // Using the manufacturer and model, get a ppd reference.
     if (!ppd_provider_->GetPpdReference(printer_manufacturer, printer_model,
                                         printer->mutable_ppd_reference())) {
@@ -255,6 +266,8 @@ void CupsPrintersHandler::OnAddedPrinter(
     std::unique_ptr<Printer> printer,
     chromeos::PrinterSetupResult result_code) {
   std::string printer_name = printer->display_name();
+  UMA_HISTOGRAM_ENUMERATION("Printing.CUPS.PrinterSetupResult", result_code,
+                            chromeos::PrinterSetupResult::kMaxValue);
   switch (result_code) {
     case chromeos::PrinterSetupResult::kSuccess: {
       auto* manager = PrintersManagerFactory::GetForBrowserContext(profile_);
@@ -407,6 +420,9 @@ void CupsPrintersHandler::OnPrintersFound(
     printers_list->Append(GetPrinterInfo(printer));
   }
 
+  UMA_HISTOGRAM_COUNTS_100("Printing.CUPS.PrintersDiscovered",

[Carlson, 2017/05/26 16:58:38]

Since this is potentially incremental, Would  it be better to record this in
OnDiscoveryInitialScanDone()? It's not clear to me that incremental results here
are useful things to record.

[skau, 2017/05/26 17:18:02]

I forgot this is incremental.  You're right that recording the incremental
values will throw off our counts.  Is there a way to get a count after the scan
is done?  We don't seem to store the whole list.

[Carlson, 2017/05/26 17:29:19]

It's incremental, but not in the way you're thinking, I think.  :)

This can be called multiple times, but each time it is called it gets the full
list of discovered printers to-date, obsoleting any previous received list.

That's why I was suggesting OnDiscoveryInitialScanDone() as a better place to do
this.  You'll have to stash the size of the most recent printers_list in the
object to make it work, but it's not too hacky, I think.

+                           printers_list->GetSize());
+
   FireWebUIListener("on-printer-discovered", *printers_list);
 }