Fixed issue where HTML files marked as attachments were failing to download.

Downloaded HTML were being intercepted and being downloaded as Offline Pages. In cases where the headers included "Content-Disposition: attachment", the Offline Page download would fail. I have added an extra constraint when intercepting the download that excludes cases with the specified header.

Bug: 1041209
Change-Id: Ia3c3ca1db4e4526c355700ed661c390a06de2d2b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2443791
Commit-Queue: Max Curran <curranmax@chromium.org>
Auto-Submit: Max Curran <curranmax@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812957}

chrome/browser/download/chrome_download_manager_delegate.cc

@@ -98,6 +98,7 @@
 #include "chrome/browser/download/android/download_utils.h"
 #include "chrome/browser/download/android/mixed_content_download_infobar_delegate.h"
 #include "chrome/browser/infobars/infobar_service.h"
+#include "net/http/http_content_disposition.h"
 #else
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_finder.h"
@@ -689,8 +690,12 @@ bool ChromeDownloadManagerDelegate::InterceptDownloadIfApplicable(
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   // For background service downloads we don't want offline pages backend to
   // intercept the download. |is_transient| flag is used to determine whether
-  // the download corresponds to background service.
+  // the download corresponds to background service. Additionally we don't want
+  // offline pages backend to intercept html files explicitly marked as
+  // attachments.
   if (!is_transient &&
+      !net::HttpContentDisposition(content_disposition, std::string())
+           .is_attachment() &&
       offline_pages::OfflinePageUtils::CanDownloadAsOfflinePage(url,
                                                                 mime_type)) {
     offline_pages::OfflinePageUtils::ScheduleDownload(

chrome/browser/download/chrome_download_manager_delegate_unittest.cc

@@ -870,6 +870,11 @@ TEST_F(ChromeDownloadManagerDelegateTest, InterceptDownloadByOfflinePages) {
   should_intercept = delegate()->InterceptDownloadIfApplicable(
       kUrl, "", "", mime_type, "", 10, true /*is_transient*/, nullptr);
   EXPECT_FALSE(should_intercept);
+
+  should_intercept = delegate()->InterceptDownloadIfApplicable(
+      kUrl, "", "attachment" /*content_disposition*/, mime_type, "", 10,
+      false /*is_transient*/, nullptr);
+  EXPECT_FALSE(should_intercept);
 }
 #endif