add tab animations

	http://b/issue?id=3053093
	first part: animate adding new tab
	animate removing tab

Change-Id: I26510e680dd005aa3fce694087fd95cbba1668a1
diff --git a/res/values/integers.xml b/res/values/integers.xml
index 9aae216..7508e00 100644
--- a/res/values/integers.xml
+++ b/res/values/integers.xml
@@ -18,4 +18,6 @@
     <integer name="max_suggest_lines_portrait">12</integer>
     <!--  The maximum number of open tabs -->
     <integer name="max_tabs">16</integer>
+    <!--  The duration of the tab animations in millisecs  -->
+    <integer name="tab_animation_duration">500</integer>
 </resources>
\ No newline at end of file