Bug 1148197 - Move share overlay margins to child to properly align. r=liuche

When it's on the parent of the outermost container with
layout_width="match_parent", the margin adds to the parent's size
(i.e. the screen width). Adding the margin to the child ensures the width is
reduced and content centered.

--HG--
extra : rebase_source : 711e8af15b1ca505aca699ea6f1ad437a6ef4ed5

mobile/android/base/resources/layout/overlay_share_dialog.xml

@@ -9,8 +9,6 @@
     android:id="@+id/sharedialog"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
-    android:layout_marginLeft="15dp"
-    android:layout_marginRight="15dp"
     android:clipChildren="false"
     android:clipToPadding="false">
 
@@ -18,6 +16,8 @@
         android:layout_width="300dp"
         android:layout_height="wrap_content"
         android:layout_gravity="bottom|center"
+        android:layout_marginLeft="15dp"
+        android:layout_marginRight="15dp"
         android:paddingTop="8dp"
         android:orientation="vertical">