[NTP OptOut] RTL support for expandable header text

Bug: 821462
Change-Id: I35159f00ec55c97a89caef1802edcdfe42e4963c
Reviewed-on: https://chromium-review.googlesource.com/972190Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Becky Zhou <huayinz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544613}

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

@@ -17,6 +17,7 @@
         android:layout_width="0dp"
         android:layout_height="wrap_content"
         android:layout_weight="1"
+        android:textAlignment="viewStart"
         android:textAppearance="@style/BlackCaption" />
 
     <org.chromium.chrome.browser.widget.TintedImageView