Add proguard configuration to support design demos sample app

Proguard was stripping out the coordinator layout behavior and the
linear layout manager classes.

Change-Id: Ibe72d5952bee20cf386e7384e261f46eea1cb67d
diff --git a/samples/SupportDesignDemos/Android.mk b/samples/SupportDesignDemos/Android.mk
index f70b6e1..96068ee 100644
--- a/samples/SupportDesignDemos/Android.mk
+++ b/samples/SupportDesignDemos/Android.mk
@@ -37,4 +37,5 @@
         --extra-packages android.support.v7.appcompat \
         --extra-packages android.support.v7.recyclerview \
         --extra-packages android.support.design
+LOCAL_PROGUARD_FLAG_FILES := proguard.flags
 include $(BUILD_PACKAGE)
diff --git a/samples/SupportDesignDemos/proguard.flags b/samples/SupportDesignDemos/proguard.flags
new file mode 100644
index 0000000..9ebd737
--- /dev/null
+++ b/samples/SupportDesignDemos/proguard.flags
@@ -0,0 +1,7 @@
+-keep public class * extends android.support.design.widget.CoordinatorLayout$Behavior {
+    public <init>(android.content.Context, android.util.AttributeSet);
+}
+
+-keep public class * extends android.support.v7.widget.LinearLayoutManager {
+    public <init>(android.content.Context, android.util.AttributeSet, int, int);
+}