Fix OMA download through context menu

For OMA downloads, chrome doesn't handle it correctly as the file needs to be converted to a .fl file and encrypted on the device.
The android DownloadManager provides such covertion.
As a result, we need to provide a way for us to intercept certain OMA downloads

BUG=382698

Review URL: https://codereview.chromium.org/571613002

Cr-Commit-Position: refs/heads/master@{#294676}

chrome/android/java/src/org/chromium/chrome/browser/contextmenu/ChromeContextMenuItemDelegate.java

@@ -31,10 +31,11 @@ public interface ChromeContextMenuItemDelegate {
 
     /**
      * Called when the context menu is trying to start a download.
+     * @param url Url of the download item.
      * @param isLink Whether or not the download is a link (as opposed to an image/video).
      * @return       Whether or not a download should actually be started.
      */
-    boolean startDownload(boolean isLink);
+    boolean startDownload(String url, boolean isLink);
 
     /**
      * Called when the {@code url} should be opened in a new tab with the same incognito state as

chrome/android/java/src/org/chromium/chrome/browser/contextmenu/ChromeContextMenuPopulator.java

@@ -115,9 +115,13 @@ public class ChromeContextMenuPopulator implements ContextMenuPopulator {
             mDelegate.onSaveToClipboard(params.getLinkText(), false);
         } else if (itemId == R.id.contextmenu_save_image ||
                 itemId == R.id.contextmenu_save_video) {
-            if (mDelegate.startDownload(false)) helper.startContextMenuDownload(false);
+            if (mDelegate.startDownload(params.getSrcUrl(), false)) {
+                helper.startContextMenuDownload(false);
+            }
         } else if (itemId == R.id.contextmenu_save_link_as) {
-            if (mDelegate.startDownload(true)) helper.startContextMenuDownload(true);
+            if (mDelegate.startDownload(params.getUnfilteredLinkUrl(), true)) {
+                helper.startContextMenuDownload(true);
+            }
         } else if (itemId == R.id.contextmenu_search_by_image) {
             mDelegate.onSearchByImageInNewTab();
         } else if (itemId == R.id.contextmenu_copy_image) {

chrome/android/java/src/org/chromium/chrome/browser/contextmenu/EmptyChromeContextMenuItemDelegate.java

@@ -27,7 +27,7 @@ public class EmptyChromeContextMenuItemDelegate implements ChromeContextMenuItem
     }
 
     @Override
-    public boolean startDownload(boolean isLink) {
+    public boolean startDownload(String url, boolean isLink) {
         return false;
     }