Use DownloadManager to download non-html res when download icon pressed

chrome/browser/android/offline_pages/downloads/offline_page_download_bridge.cc

Index: chrome/browser/android/offline_pages/downloads/offline_page_download_bridge.cc
diff --git a/chrome/browser/android/offline_pages/downloads/offline_page_download_bridge.cc b/chrome/browser/android/offline_pages/downloads/offline_page_download_bridge.cc
index 928418495a72cce89553fd27e0f3a02693f18b20..2c7b730135b76744e7399cb7cf7f08e3de05cc44 100644
--- a/chrome/browser/android/offline_pages/downloads/offline_page_download_bridge.cc
+++ b/chrome/browser/android/offline_pages/downloads/offline_page_download_bridge.cc
@@ -28,6 +28,9 @@
 #include "components/offline_pages/core/offline_page_feature.h"
 #include "components/offline_pages/core/offline_page_model.h"
 #include "content/public/browser/browser_context.h"
+#include "content/public/browser/download_manager.h"
+#include "content/public/browser/download_url_parameters.h"
+#include "content/public/browser/navigation_entry.h"
 #include "content/public/browser/web_contents.h"
 #include "jni/OfflinePageDownloadBridge_jni.h"
 #include "net/base/filename_util.h"
@@ -337,10 +340,35 @@ void OfflinePageDownloadBridge::StartDownload(
     return;
 
   GURL url = web_contents->GetLastCommittedURL();
+  if (url.is_empty())
+    return;
+
   GURL original_url =
       offline_pages::OfflinePageUtils::GetOriginalURLFromWebContents(
           web_contents);
 
+  // If the page is not a HTML page, route to DownloadManager.
+  if (!offline_pages::OfflinePageUtils::CanDownloadAsOfflinePage(
+          web_contents->GetContentsMimeType())) {
+    content::DownloadManager* dlm = content::BrowserContext::GetDownloadManager(
+        web_contents->GetBrowserContext());
+    std::unique_ptr<content::DownloadUrlParameters> dl_params(
+        content::DownloadUrlParameters::CreateForWebContentsMainFrame(
+            web_contents, url));
+
+    content::NavigationEntry* entry =
+        web_contents->GetController().GetLastCommittedEntry();
+    DCHECK(entry);

[Dmitry Titov, 2017/04/27 23:02:45]

I'd just do if(!entry) return here...
Otherwise it looks like a crash you sometimes expect.

[jianli, 2017/04/28 00:21:59]

GetLastCommittedURL should return an empty URL if the entry does not exist. So I
added a check at line 343. Using DCHECK here should be safe.

+    content::Referrer referrer =
+        content::Referrer::SanitizeForRequest(url, entry->GetReferrer());
+    dl_params->set_referrer(referrer);
+
+    dl_params->set_prefer_cache(true);
+    dl_params->set_prompt(false);
+    dlm->DownloadUrl(std::move(dl_params));
+    return;
+  }
+
   ScopedJavaGlobalRef<jobject> j_tab_ref(env, j_tab);
 
   OfflinePageUtils::CheckDuplicateDownloads(