Add sampling of unknown filetypes in download protection.

chrome/browser/safe_browsing/download_protection_service.h

Index: chrome/browser/safe_browsing/download_protection_service.h
diff --git a/chrome/browser/safe_browsing/download_protection_service.h b/chrome/browser/safe_browsing/download_protection_service.h
index 83ed3596582f8b377d946503aa4e964a94bfbeb4..181e5b18606c885d0038bef5cea4235b0874de41 100644
--- a/chrome/browser/safe_browsing/download_protection_service.h
+++ b/chrome/browser/safe_browsing/download_protection_service.h
@@ -107,8 +107,9 @@ class DownloadProtectionService {
 
   // Returns true iff the download specified by |info| should be scanned by
   // CheckClientDownload() for malicious content.
-  virtual bool IsSupportedDownload(const content::DownloadItem& item,
-                                   const base::FilePath& target_path) const;
+  virtual bool IsSupportedDownload(
+      const content::DownloadItem& item,
+      const base::FilePath& target_path) const;
 
   virtual void CheckPPAPIDownloadRequest(
       const GURL& requestor_url,
@@ -157,7 +158,7 @@ class DownloadProtectionService {
 
  protected:
   // Enum to keep track why a particular download verdict was chosen.
-  // This is used to keep some stats around.
+  // Used for UMA metrics. Do not reorder.
   enum DownloadCheckResultReason {
     REASON_INVALID_URL,
     REASON_SB_DISABLED,
@@ -183,6 +184,7 @@ class DownloadProtectionService {
     REASON_DOWNLOAD_POTENTIALLY_UNWANTED,
     REASON_UNSUPPORTED_URL_SCHEME,
     REASON_MANUAL_BLACKLIST,
+    REASON_SAMPLED_UNSUPPORTED_FILE,
     REASON_MAX  // Always add new values before this one.
   };