Make preview size smaller so that low-res images come in faster.

Change-Id: I82fea176a2aa8b0a3abfd829c0ec2d16f267ef5b
diff --git a/res/values/dimens.xml b/res/values/dimens.xml
index 7cc4be4..f2ad88f 100644
--- a/res/values/dimens.xml
+++ b/res/values/dimens.xml
@@ -94,7 +94,7 @@
     <dimen name="zoom_font_size">14pt</dimen>
     <dimen name="shutter_offset">-22dp</dimen>
     <dimen name="size_thumbnail">200dip</dimen>
-    <dimen name="size_preview">600dip</dimen>
+    <dimen name="size_preview">400dip</dimen>
     <dimen name="navigation_bar_height">48dip</dimen>
     <dimen name="navigation_bar_width">42dip</dimen>
     <dimen name="capture_size">48dip</dimen>