Force AlertDialogLayout to have gravity start|top

AlertDialogLayout overrides LinearLayout#onMeasure but not onLayout,
meaning that some state initialized for the handling of gravity may
not be valid in LinearLayout#onLayout. As this is an internal class
never used directly by apps, explicitly specify the default gravity of
start|top in @layout/alert_dialog_material to avoid this bug. Apps
that do things like set gravity in their theme (for whatever reason)
could otherwise change its behavior.

Bug 30494039

Change-Id: I71a8be1829a7fe24cf7714a3bd5ed732f85eb887
(cherry picked from commit 39e0bf23f50a3de112b232321c5e0a1013af70c7)
(cherry picked from commit 00c4f7ba652a817f208fb761feb8c6a063da848a)
diff --git a/core/res/res/layout/alert_dialog_material.xml b/core/res/res/layout/alert_dialog_material.xml
index 6d33de6..178505c 100644
--- a/core/res/res/layout/alert_dialog_material.xml
+++ b/core/res/res/layout/alert_dialog_material.xml
@@ -20,6 +20,7 @@
     android:id="@+id/parentPanel"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
+    android:gravity="start|top"
     android:orientation="vertical">
 
     <include layout="@layout/alert_dialog_title_material" />