Remove obsolete download security metrics

Download.Started.ContentType.InsecureChain and
Download.Started.ContentType.SecureChain have been superseded by the
new mixed downloads metrics under Download.InsecureBlocking, so this
marks the old histograms as obsolete and removes the collection code.

Bug: 1063890
Change-Id: I957d55299c302a3e49b5be5923180858eec1a007
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2140296
Reviewed-by: Min Qin <qinmin@chromium.org>
Commit-Queue: Christopher Thompson <cthomp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#757470}

components/download/internal/common/download_stats.cc

@@ -734,32 +734,6 @@ void RecordDownloadValidationMetrics(DownloadMetricsCallsite callsite,
       DownloadContent::MAX);
 }
 
-void RecordDownloadContentTypeSecurity(
-    const GURL& download_url,
-    const std::vector<GURL>& url_chain,
-    const std::string& mime_type,
-    const base::RepeatingCallback<bool(const GURL&)>&
-        is_origin_secure_callback) {
-  bool is_final_download_secure = is_origin_secure_callback.Run(download_url);
-  bool is_redirect_chain_secure = true;
-  for (const auto& url : url_chain) {
-    if (!is_origin_secure_callback.Run(url)) {
-      is_redirect_chain_secure = false;
-      break;
-    }
-  }
-
-  DownloadContent download_content =
-      download::DownloadContentFromMimeType(mime_type, false);
-  if (is_final_download_secure && is_redirect_chain_secure) {
-    UMA_HISTOGRAM_ENUMERATION("Download.Start.ContentType.SecureChain",
-                              download_content, DownloadContent::MAX);
-  } else {
-    UMA_HISTOGRAM_ENUMERATION("Download.Start.ContentType.InsecureChain",
-                              download_content, DownloadContent::MAX);
-  }
-}
-
 void RecordDownloadSourcePageTransitionType(
     const base::Optional<ui::PageTransition>& page_transition) {
   if (!page_transition)

components/download/internal/common/in_progress_download_manager.cc

@@ -487,11 +487,6 @@ void InProgressDownloadManager::StartDownload(
   std::vector<GURL> url_chain = info->url_chain;
   std::string mime_type = info->mime_type;
 
-  if (info->is_new_download) {
-    RecordDownloadContentTypeSecurity(info->url(), info->url_chain,
-                                      info->mime_type, is_origin_secure_cb_);
-  }
-
   // If the download cannot be found locally, ask |delegate_| to provide the
   // DownloadItem.
   if (delegate_ && !GetDownloadByGuid(info->guid)) {

components/download/public/common/download_stats.h

@@ -420,13 +420,6 @@ COMPONENTS_DOWNLOAD_EXPORT void RecordDownloadConnectionSecurity(
     const GURL& download_url,
     const std::vector<GURL>& url_chain);
 
-COMPONENTS_DOWNLOAD_EXPORT void RecordDownloadContentTypeSecurity(
-    const GURL& download_url,
-    const std::vector<GURL>& url_chain,
-    const std::string& mime_type,
-    const base::RepeatingCallback<bool(const GURL&)>&
-        is_origin_secure_callback);
-
 COMPONENTS_DOWNLOAD_EXPORT void RecordDownloadSourcePageTransitionType(
     const base::Optional<ui::PageTransition>& transition);
 

tools/metrics/histograms/histograms.xml

@@ -43063,6 +43063,10 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 
 <histogram name="Download.Start.ContentType.InsecureChain"
     enum="DownloadContentType" expires_after="2020-09-06">
+  <obsolete>
+    Removed in 04/2020. Superseded by mixed download metrics under
+    Download.InsecureBlocking.
+  </obsolete>
   <owner>cthomp@chromium.org</owner>
   <owner>estark@chromium.org</owner>
   <summary>
@@ -43086,6 +43090,10 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 
 <histogram name="Download.Start.ContentType.SecureChain"
     enum="DownloadContentType" expires_after="2020-05-03">
+  <obsolete>
+    Removed in 04/2020. Superseded by mixed download metrics under
+    Download.InsecureBlocking.
+  </obsolete>
   <owner>cthomp@chromium.org</owner>
   <owner>estark@chromium.org</owner>
   <summary>