Background download: Delete hash histogram.

This CL deletes histogram Download.Service.Finish.ReportedHash. Over
99% of background downloads have hash, it's not very actionable.

Bug: 995485
Change-Id: I1176f5d37d608e99eba0acf8fdfa50ea938d5569
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1803880Reviewed-by: Min Qin <qinmin@chromium.org>
Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
Reviewed-by: Nik Bhagat <nikunjb@chromium.org>
Commit-Queue: Xing Liu <xingliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#697769}

components/download/internal/background_service/controller_impl.cc

@@ -1153,7 +1153,6 @@ void ControllerImpl::HandleCompleteDownload(CompletionType type,
     DCHECK(driver_entry.has_value());
     stats::LogFilePathRenamed(driver_entry->current_file_path !=
                               entry->target_file_path);
-    stats::LogHashPresence(!driver_entry->hash256.empty());
     entry->target_file_path = driver_entry->current_file_path;
     entry->completion_time = driver_entry->completion_time;
     entry->bytes_downloaded = driver_entry->bytes_downloaded;

components/download/internal/background_service/stats.cc

@@ -330,10 +330,6 @@ void LogHasUploadData(DownloadClient client, bool has_upload_data) {
   base::UmaHistogramBoolean(name, has_upload_data);
 }
 
-void LogHashPresence(bool hash_exists) {
-  UMA_HISTOGRAM_BOOLEAN("Download.Service.Finish.ReportedHash", hash_exists);
-}
-
 void LogDownloadClientInflatedFullBrowser(DownloadClient client) {
   std::string client_name(ClientToHistogramSuffix(client));
   base::UmaHistogramBoolean(

components/download/internal/background_service/stats.h

@@ -220,9 +220,6 @@ void LogEntryRetryCount(uint32_t retry_count);
 // Records whether the entry was an upload.
 void LogHasUploadData(DownloadClient client, bool has_upload_data);
 
-// Records whether or not a completed entry has a hash value.
-void LogHashPresence(bool hash_exists);
-
 // Records count of reduced mode to full browser transitions requested by each
 // client.
 void LogDownloadClientInflatedFullBrowser(DownloadClient client);

tools/metrics/histograms/histograms.xml

@@ -34302,6 +34302,9 @@ uploading your change for review.
 
 <histogram name="Download.Service.Finish.ReportedHash"
     enum="BooleanIncludesHash" expires_after="2019-10-01">
+  <obsolete>
+    Deprecated in 09/2019.
+  </obsolete>
   <owner>dtrainor@chromium.org</owner>
   <owner>xingliu@chromium.org</owner>
   <summary>