Enable asset tasks when using gradle to process resources.

build/android/gradle/android.jinja

 {# Copyright 2016 The Chromium Authors. All rights reserved. #}
 {# Use of this source code is governed by a BSD-style license that can be #}
 {# found in the LICENSE file. #}
 {% macro expand_sourceset(variables, prefix) %}
 {% if variables is defined %}
         {{ prefix }} {
             manifest.srcFile "{{ variables.android_manifest }}"
             java.srcDirs = [
 {% for path in variables.java_dirs %}
                 "{{ path }}",
@@ skipping 59 matching lines @@
 android.variantFilter { variant ->
     if (variant.buildType.name.equals('release')) {
         variant.setIgnore(true);
     }
 }
 
 afterEvaluate {
     def tasksToDisable = tasks.findAll {
         return (it.name.equals('generateDebugSources')  // causes unwanted AndroidManifest.java
                 || it.name.equals('generateReleaseSources')
+{% if not use_gradle_process_resources %}
                 || it.name.endsWith('Assets')
+{% endif %}
                 || it.name.endsWith('BuildConfig')  // causes unwanted BuildConfig.java
 {% if not use_gradle_process_resources %}
                 || it.name.endsWith('Resources')
                 || it.name.endsWith('ResValues')
 {% endif %}
                 || it.name.endsWith('Aidl')
                 || it.name.endsWith('Renderscript')
                 || it.name.endsWith('Shaders'))
     }
     tasksToDisable.each { Task task ->
       task.enabled = false
     }
 }