[NTP Snippets] 📷 Add placeholders and start caching thumbnails

chrome/android/java/res/layout/new_tab_page_snippets_card.xml

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Copyright 2015 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. -->
 
 <RelativeLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:id="@+id/snippets_card_view"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
@@ skipping 28 matching lines @@
         android:id="@+id/article_publisher"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:layout_below="@+id/article_snippet"
         android:layout_toStartOf="@+id/article_thumbnail"
         android:layout_marginTop="16dp"
         android:maxLines="1"
         android:ellipsize="end"
         android:textSize="14sp"
         android:textColor="@color/snippets_publisher_name_color" />
-        
+
     <ImageView
         android:id="@+id/article_thumbnail"
+        android:background="@color/snippets_thumnail_placeholder_bg"
         android:layout_width="@dimen/snippets_thumbnail_size"
         android:layout_height="@dimen/snippets_thumbnail_size"
         android:layout_alignParentTop="true"
         android:layout_alignParentEnd="true"
         android:layout_marginStart="16dp"
         android:scaleType="centerCrop"
         android:contentDescription="@null"

[Theresa, 2016/04/11 23:42:27]

Does the content description get set elsewhere? This is important for
accessibility.

[dgn, 2016/04/12 11:17:14]

Not as far as I can see. That being said, it's content that is not actionable
and can't really be described. I can't think of a description here that would be
meaningful and not just end up being noise. ("thumbnail", "thumbnail",
"thumbnail" ...) Any idea?

[Theresa, 2016/04/12 18:11:48]

As long as the snippet itself has a content description I think that's fine. Can
you test with talk back on please to see what gets read out for the snippet?

Since this has no content description, it would be good to confirm that the
thumbnail can't get focus for accessibility. This might need
android:importantForAccessibility="no" or android:focusableInTouchMode="false".

[dgn, 2016/04/13 16:52:21]

TalkBack properly skips it. Looking on the net, it looks like screen readers
skipping entirely elements with the @null description is the expected behaviour.
Other concern, thew full card only can be selected. individual text fields
inside it are not selectable in TalkBack mode, so it just reads everything at
once. That's weird but we are planning to have a complete a11y pass on the whole
new UI, so it should be addressed then.

[Theresa, 2016/04/13 16:53:09]

sg, thanks for testing :)

         android:src="@null"/>
 </RelativeLayout>