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..55dd7fecbeff13f21ba1ae1ada2d8e810b05910b 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;
@@ -206,6 +210,10 @@ const DownloadPathReservationTracker::FilenameConflictAction
     kDefaultPlatformConflictAction = DownloadPathReservationTracker::UNIQUIFY;
 #endif
 
+#if BUILDFLAG(ENABLE_PLUGINS)
+constexpr char kPDFMimeType[] = "application/pdf";
+#endif
+
 }  // namespace
 
 ChromeDownloadManagerDelegate::ChromeDownloadManagerDelegate(Profile* profile)
@@ -283,6 +291,13 @@ void ChromeDownloadManagerDelegate::ReturnNextId(
 bool ChromeDownloadManagerDelegate::DetermineDownloadTarget(
     DownloadItem* download,
     const content::DownloadTargetCallback& callback) {
+#if BUILDFLAG(ENABLE_PLUGINS)
+  if (download->GetTargetFilePath().empty() &&
+      download->GetMimeType() == kPDFMimeType && !download->HasUserGesture()) {
+    ReportPDFLoadStatus(PDFLoadStatus::TRIGGERED_NO_GESTURE_DRIVE_BY_DOWNLOAD);
+  }
+#endif
+
   DownloadTargetDeterminer::CompletionCallback target_determined_callback =
       base::Bind(&ChromeDownloadManagerDelegate::OnDownloadTargetDetermined,
                  weak_ptr_factory_.GetWeakPtr(),