Add DownloadStatus metric to FaviconHandler

components/favicon/core/favicon_handler.h

Index: components/favicon/core/favicon_handler.h
diff --git a/components/favicon/core/favicon_handler.h b/components/favicon/core/favicon_handler.h
index 9e6e22b9f97126bc1762aa49db194d4225a8f635..9e5af6297d3b70ddaa51334350cf8f343a4eeb09 100644
--- a/components/favicon/core/favicon_handler.h
+++ b/components/favicon/core/favicon_handler.h
@@ -75,6 +75,19 @@ class FaviconService;
 
 class FaviconHandler {
  public:
+  // Outcome of a favicon download.
+  // Recorded as Favicons.DownloadOutcome and public for testing.
+  //
+  // These values must stay in sync with the FaviconDownloadStatus enum
+  // in histograms.xml and should be treated as append-only, since it backs an
+  // UMA histogram..
+  enum class DownloadOutcome {
+    SUCCEEDED = 0,
+    FAILED = 1,
+    SKIPPED = 2,
+    DOWNLOAD_OUTCOME_COUNT = 3
+  };
+
   class Delegate {
    public:
     // Mimics WebContents::ImageDownloadCallback.
@@ -290,6 +303,10 @@ class FaviconHandler {
   // This handler's delegate.
   Delegate* delegate_;
 
+  // Captures the number of download requests that were initiated for the
+  // current url_.
+  int num_download_requests_;
+
   // The index of the favicon URL in |image_urls_| which is currently being
   // requested from history or downloaded.
   size_t current_candidate_index_;