PDF: Add UMA to track successful / failed PDF loads

chrome/renderer/plugins/plugin_uma.h

Index: chrome/renderer/plugins/plugin_uma.h
diff --git a/chrome/renderer/plugins/plugin_uma.h b/chrome/renderer/plugins/plugin_uma.h
index b29e9dc31c641f59bfaa375bd541440ae03d8582..21d209bc7976cd7a275a88a3dc2fcb9027df845d 100644
--- a/chrome/renderer/plugins/plugin_uma.h
+++ b/chrome/renderer/plugins/plugin_uma.h
@@ -22,7 +22,7 @@ class PluginUMAReporter {
  public:
   enum ReportType {
     MISSING_PLUGIN,
-    DISABLED_PLUGIN
+    DISABLED_PLUGIN,
   };
 
   // Make sure the enum list in tools/histogram/histograms.xml is updated with
@@ -44,6 +44,14 @@ class PluginUMAReporter {
     PLUGIN_TYPE_MAX
   };
 
+  // Must be kept in sync with PDFLoadStatus enum in histograms.xml.

[Ilya Sherman, 2017/05/08 17:59:57]

Please also document that this enum should be treated as append-only, since we
want time-invariant semantics for the histogram buckets.

[tommycli, 2017/05/08 18:16:17]

Done.

+  enum PDFLoadStatus {
+    LOADED_FULL_PAGE_PDF_WITH_PDFIUM = 0,
+    LOADED_EMBEDDED_PDF_WITH_PDFIUM = 1,
+    SHOWED_DISABLED_PLUGIN_PLACEHOLDER_FOR_EMBEDDED_PDF = 2,
+    PDF_LOAD_STATUS_MAX

[Ilya Sherman, 2017/05/08 17:59:57]

Optional nit: Typically, "max" is used as an alias for the last item in the
enum, whereas "count" is used to count the number of valid entries in the enum. 
So, I'd recommend "count" here.

[tommycli, 2017/05/08 18:16:17]

Done.

+  };
+
   // Sends UMA data, i.e. plugin's type.
   class UMASender {
    public:
@@ -55,6 +63,8 @@ class PluginUMAReporter {
   // Returns singleton instance.
   static PluginUMAReporter* GetInstance();
 
+  static void ReportPDFLoadStatus(PDFLoadStatus status);
+
   void ReportPluginMissing(const std::string& plugin_mime_type,
                            const GURL& plugin_src);