Isolate initiation counts for downloads to their own histograms and improve

chrome/browser/download/download_util.h

Index: chrome/browser/download/download_util.h
diff --git a/chrome/browser/download/download_util.h b/chrome/browser/download/download_util.h
index 6df96e46bce3154890153569f2d26c8d227da0f9..a2cfc4e85a30fb10a532d7173fcef7aea574c46e 100644
--- a/chrome/browser/download/download_util.h
+++ b/chrome/browser/download/download_util.h
@@ -174,23 +174,51 @@ void RecordShelfClose(int size, int in_progress, bool autoclose);
 // Used for counting UMA stats. Similar to content's
 // download_stats::DownloadCountTypes but from the chrome layer.
 enum ChromeDownloadCountTypes {
+  // A download *would* have been initiated, but it was blocked
+  // by the DownloadThrottlingResourceHandler.
+  BLOCKED_BY_THROTTLING = 0,
+
+  // The "= 2" is to get around a feature of the histogram system
+  // which puts a floor of 1 for the minimum value for enum histograms
+  // to allow there to be a bucket for values outside the expected range.
+  // This isn't ideal since many (possibly most) enum histograms start
+  // at zero, but there isn't any practical negative effect in UMA;
+  // the zero value just uses the underflow bucket.  However, if
+  // a histogram only has one entry, it does result in a DCHECK because
+  // the maximum value of the histogram is greater than the minimum value.
+  // We solve this by bumping up the maximum value.  This assignment
+  // can be removed if any entries are added to this enum in the
+  // future.
+  CHROME_DOWNLOAD_COUNT_TYPES_LAST_ENTRY = 2
+};
+
+// Used for counting UMA stats. Similar to content's
+// download_stats::DownloadInitiattionSources but from the chrome layer.
+enum ChromeDownloadSource {
   // The download was initiated by navigating to a URL (e.g. by user click).
-  INITIATED_BY_NAVIGATION_COUNT = 0,
+  INITIATED_BY_NAVIGATION = 0,
 
   // The download was initiated by invoking a context menu within a page.
-  INITIATED_BY_CONTEXT_MENU_COUNT,
+  INITIATED_BY_CONTEXT_MENU,
 
   // The download was initiated by the WebStore installer.
-  INITIATED_BY_WEBSTORE_INSTALLER_COUNT,
+  INITIATED_BY_WEBSTORE_INSTALLER,
 
   // The download was initiated by the ImageBurner (cros).
-  INITIATED_BY_IMAGE_BURNER_COUNT,
+  INITIATED_BY_IMAGE_BURNER,
 
-  DOWNLOAD_COUNT_TYPES_LAST_ENTRY,
+  // The download was initiated by the plugin installer.
+  INITIATED_BY_PLUGIN_INSTALLER,
+
+  CHROME_DOWNLOAD_SOURCE_LAST_ENTRY,
 };
 
+// Increment one of the above counts.
 void RecordDownloadCount(ChromeDownloadCountTypes type);
 
+// Record initiation of a download from a specific source.
+void RecordDownloadSource(ChromeDownloadSource source);
+
 }  // namespace download_util
 
 #endif  // CHROME_BROWSER_DOWNLOAD_DOWNLOAD_UTIL_H_