Fix an issue that android doesn't know how to open the download after completion

chrome/android/java/src/org/chromium/chrome/browser/download/ChromeDownloadDelegate.java

Index: chrome/android/java/src/org/chromium/chrome/browser/download/ChromeDownloadDelegate.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/download/ChromeDownloadDelegate.java b/chrome/android/java/src/org/chromium/chrome/browser/download/ChromeDownloadDelegate.java
index 2a4998b170ff666e41621ed4427d4ff4df819aa9..db9af9cb7a740b96e5315b5afccdc3ed4ccc9d86 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/download/ChromeDownloadDelegate.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/download/ChromeDownloadDelegate.java
@@ -510,13 +510,14 @@ public class ChromeDownloadDelegate {
      * @param filename file name obtained from content disposition header
      * @return The MIME type that should be used for this data.
      */
-    private static String remapGenericMimeType(String mimeType, String url, String filename) {
+    static String remapGenericMimeType(String mimeType, String url, String filename) {
         // If we have one of "generic" MIME types, try to deduce
         // the right MIME type from the file extension (if any):
         if (mimeType == null || mimeType.isEmpty() || "text/plain".equals(mimeType)
                 || "application/octet-stream".equals(mimeType)
                 || "octet/stream".equals(mimeType)
-                || "application/force-download".equals(mimeType)) {
+                || "application/force-download".equals(mimeType)
+                || "application/unknown".equals(mimeType)) {
 
             if (!TextUtils.isEmpty(filename)) {
                 url = filename;