Add dialogCornerRadius support

dialogCornerRadius is a new platform attr and should
be available in the supportlib.

Test: visual. support-v7-demos
Bug: 69308766
Change-Id: If92675364260b80b52d4ad8753987d71cec4e725
diff --git a/v7/appcompat/res/values/attrs.xml b/v7/appcompat/res/values/attrs.xml
index 2012a3a..485d92b 100644
--- a/v7/appcompat/res/values/attrs.xml
+++ b/v7/appcompat/res/values/attrs.xml
@@ -189,6 +189,8 @@
         <attr name="dialogPreferredPadding" format="dimension" />
         <!-- The list divider used in alert dialogs. -->
         <attr name="listDividerAlertDialog" format="reference" />
+        <!-- Preferred corner radius of dialogs. -->
+        <attr name="dialogCornerRadius" format="dimension" />
 
         <!-- =================== -->
         <!-- Other widget styles -->