Add UMA to record why chrome shows generic warning

chrome/browser/download/chrome_download_manager_delegate.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/download/chrome_download_manager_delegate.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/callback.h"
 #include "base/files/file_util.h"
 #include "base/macros.h"
+#include "base/metrics/histogram.h"
 #include "base/rand_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/task_runner.h"
 #include "base/task_runner_util.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/download/download_completion_blocker.h"
@@ skipping 150 matching lines @@
 
 #endif  // FULL_SAFE_BROWSING
 
 // Called on the blocking pool to determine the MIME type for |path|.
 std::string GetMimeType(const base::FilePath& path) {
   std::string mime_type;
   net::GetMimeTypeFromFile(path, &mime_type);
   return mime_type;
 }
 
+// Reason for why danger type is DOWNLOAD_DANGER_TYPE_DANGEROUS_FILE.
+// Used by "Download.DangerousFile.Reason" UMA metric.
+// Do not change the ordering or remove items.
+enum DangerousFileReason {
+  SB_NOT_AVAILABLE = 0,
+  SB_RETURNS_UNKOWN = 1,
+  SB_RETURNS_SAFE = 2,
+  DANGEROUS_FILE_REASON_MAX
+};
+
 }  // namespace
 
 ChromeDownloadManagerDelegate::ChromeDownloadManagerDelegate(Profile* profile)
     : profile_(profile),
       next_download_id_(content::DownloadItem::kInvalidId),
       download_prefs_(new DownloadPrefs(profile)),
       weak_ptr_factory_(this) {
 }
 
 ChromeDownloadManagerDelegate::~ChromeDownloadManagerDelegate() {
@@ skipping 136 matching lines @@
     content::DownloadDangerType danger_type = item->GetDangerType();
     if (DownloadItemModel(item).GetDangerLevel() !=
             DownloadFileType::NOT_DANGEROUS &&
         (danger_type == content::DOWNLOAD_DANGER_TYPE_NOT_DANGEROUS ||
          danger_type ==
              content::DOWNLOAD_DANGER_TYPE_MAYBE_DANGEROUS_CONTENT)) {
       DVLOG(2) << __FUNCTION__
                << "() SB service disabled. Marking download as DANGEROUS FILE";
       item->OnContentCheckCompleted(
           content::DOWNLOAD_DANGER_TYPE_DANGEROUS_FILE);
+      UMA_HISTOGRAM_ENUMERATION("Download.DangerousFile.Reason",
+                                SB_NOT_AVAILABLE, DANGEROUS_FILE_REASON_MAX);
       content::BrowserThread::PostTask(content::BrowserThread::UI, FROM_HERE,
                                        internal_complete_callback);
       return false;
     }
   } else if (!state->is_complete()) {
     // Don't complete the download until we have an answer.
     state->set_callback(internal_complete_callback);
     return false;
   }
 
@@ skipping 329 matching lines @@
   // has not been set to DANGEROUS yet.  We don't want to show two warnings.
   if (item->GetDangerType() == content::DOWNLOAD_DANGER_TYPE_NOT_DANGEROUS ||
       item->GetDangerType() ==
       content::DOWNLOAD_DANGER_TYPE_MAYBE_DANGEROUS_CONTENT) {
     content::DownloadDangerType danger_type =
         content::DOWNLOAD_DANGER_TYPE_NOT_DANGEROUS;
     switch (result) {
       case DownloadProtectionService::UNKNOWN:
         // The check failed or was inconclusive.
         if (DownloadItemModel(item).GetDangerLevel() !=
-            DownloadFileType::NOT_DANGEROUS)
+            DownloadFileType::NOT_DANGEROUS) {
           danger_type = content::DOWNLOAD_DANGER_TYPE_DANGEROUS_FILE;
+          UMA_HISTOGRAM_ENUMERATION("Download.DangerousFile.Reason",
+                                    SB_RETURNS_UNKOWN,
+                                    DANGEROUS_FILE_REASON_MAX);
+        }
         break;
       case DownloadProtectionService::SAFE:
         // If this file type require explicit consent, then set the danger type
         // to DANGEROUS_FILE so that the user be required to manually vet
         // whether the download is intended or not.
         if (DownloadItemModel(item).GetDangerLevel() ==
-            DownloadFileType::DANGEROUS)
+            DownloadFileType::DANGEROUS) {
           danger_type = content::DOWNLOAD_DANGER_TYPE_DANGEROUS_FILE;
+          UMA_HISTOGRAM_ENUMERATION("Download.DangerousFile.Reason",
+                                    SB_RETURNS_SAFE, DANGEROUS_FILE_REASON_MAX);
+        }
         break;
       case DownloadProtectionService::DANGEROUS:
         danger_type = content::DOWNLOAD_DANGER_TYPE_DANGEROUS_CONTENT;
         break;
       case DownloadProtectionService::UNCOMMON:
         danger_type = content::DOWNLOAD_DANGER_TYPE_UNCOMMON_CONTENT;
         break;
       case DownloadProtectionService::DANGEROUS_HOST:
         danger_type = content::DOWNLOAD_DANGER_TYPE_DANGEROUS_HOST;
         break;
@@ skipping 80 matching lines @@
       path.MatchesExtension(FILE_PATH_LITERAL(".xht")) ||
       path.MatchesExtension(FILE_PATH_LITERAL(".xhtm")) ||
       path.MatchesExtension(FILE_PATH_LITERAL(".xhtml")) ||
       path.MatchesExtension(FILE_PATH_LITERAL(".xsl")) ||
       path.MatchesExtension(FILE_PATH_LITERAL(".xslt"))) {
     return true;
   }
 #endif
   return false;
 }