Volume Motion: Initial show and expand transition.

Also re-enable the content collapse layout transition animations,
supported by ensuring the dialog window is tall enough for long
enough to complete the transition, avoiding clipping.

Bug: 21335976
Change-Id: Ibc4cbb1e882c1e11c4406463752afa177fb1e6d7
diff --git a/packages/SystemUI/res/values/dimens.xml b/packages/SystemUI/res/values/dimens.xml
index 869b03a..005077f 100644
--- a/packages/SystemUI/res/values/dimens.xml
+++ b/packages/SystemUI/res/values/dimens.xml
@@ -576,6 +576,9 @@
     <!-- Standard image button size for volume dialog buttons -->
     <dimen name="volume_button_size">48dp</dimen>
 
+    <!-- Volume dialog root view bottom margin, at rest -->
+    <dimen name="volume_dialog_margin_bottom">4dp</dimen>
+
     <!-- Padding between icon and text for managed profile toast -->
     <dimen name="managed_profile_toast_padding">4dp</dimen>