Add interface for requesting file access

This is needed for some features like download and local file access.

BUG=501606

Review URL: https://codereview.chromium.org/1219213002

Cr-Commit-Position: refs/heads/master@{#337110}

ui/android/java/src/org/chromium/ui/base/WindowAndroid.java

@@ -16,6 +16,7 @@
 import android.content.pm.PackageManager;
 import android.os.Build;
 import android.os.Bundle;
+import android.os.Handler;
 import android.os.Process;
 import android.util.Log;
 import android.util.SparseArray;
@@ -255,6 +256,26 @@ public void requestPermissions(String[] permissions, PermissionCallback callback
         assert false : "Failed to request permissions using a WindowAndroid without an Activity";
     }
 
+    /**
+     * Determine whether access to file is granted.
+     */
+    public boolean hasFileAccess() {
+        return true;
+    }
+
+    /**
+     * Requests the access to files.
+     * @param callback The callback to be notified whether access were granted.
+     */
+    public void requestFileAccess(final FileAccessCallback callback) {
+        new Handler().post(new Runnable() {
+            @Override
+            public void run() {
+                callback.onFileAccessResult(false);
+            }
+        });
+    }
+
     /**
      * Displays an error message with a provided error message string.
      * @param error The error message string to be displayed.
@@ -379,6 +400,17 @@ public interface PermissionCallback {
         void onRequestPermissionsResult(String[] permissions, int[] grantResults);
     }
 
+    /**
+     * Callback for file access requests.
+     */
+    public interface FileAccessCallback {
+        /**
+         * Called upon completing a file access request.
+         * @param granted Whether file access is granted.
+         */
+        void onFileAccessResult(boolean granted);
+    }
+
     /**
      * Tests that an activity is available to handle the passed in intent.
      * @param  intent The intent to check.