PDF: Add UMA to track embedded PDF triggered drive-by downloads.

chrome/browser/download/chrome_download_manager_delegate.cc

Index: chrome/browser/download/chrome_download_manager_delegate.cc
diff --git a/chrome/browser/download/chrome_download_manager_delegate.cc b/chrome/browser/download/chrome_download_manager_delegate.cc
index 37c55d6a14feb6b932b00063801f9f4caf33dbd0..e6fe6992e4e4d9231ec8a34d28268140e86e0693 100644
--- a/chrome/browser/download/chrome_download_manager_delegate.cc
+++ b/chrome/browser/download/chrome_download_manager_delegate.cc
@@ -78,6 +78,10 @@
 #include "extensions/common/constants.h"
 #endif
 
+#if BUILDFLAG(ENABLE_PLUGINS)
+#include "chrome/common/pdf_uma.h"
+#endif
+
 using content::BrowserThread;
 using content::DownloadItem;
 using content::DownloadManager;
@@ -732,6 +736,12 @@ void ChromeDownloadManagerDelegate::GetFileMimeType(
       FROM_HERE, {base::MayBlock()}, base::Bind(&GetMimeType, path), callback);
 }
 
+void ChromeDownloadManagerDelegate::RecordDriveByPDFDownload() const {
+#if BUILDFLAG(ENABLE_PLUGINS)
+  ReportPDFLoadStatus(TRIGGERED_DRIVE_BY_DOWNLOAD);
+#endif
+}
+
 #if defined(FULL_SAFE_BROWSING)
 void ChromeDownloadManagerDelegate::CheckClientDownloadDone(
     uint32_t download_id,