Rework thumbnails in activity manager.

We now only keep a thumbnail for the task, not for each
activity.  However if you use FLAG_ACTIVITY_CLEAR_WHEN_TASK_RESET,
we will make a new secondary thumbnail for that series of
activities.  There is a new API for the app to get these
secondary thumbnails.

Also set a default thumbnail size for non-xlarge screens
so we have thumbnails on phones.  (We need some smarter
code in the platform for computing the actual thumbnail
dimensions of the current device).  And add a test app
to show recent tasks + thumbnails.

Change-Id: Ic36759f6635522118a2cb7f156662229a610c492
diff --git a/tests/ActivityTests/Android.mk b/tests/ActivityTests/Android.mk
new file mode 100644
index 0000000..f3c6b5a
--- /dev/null
+++ b/tests/ActivityTests/Android.mk
@@ -0,0 +1,11 @@
+LOCAL_PATH:= $(call my-dir)
+include $(CLEAR_VARS)
+
+LOCAL_SRC_FILES := $(call all-subdir-java-files)
+
+LOCAL_PACKAGE_NAME := ActivityTest
+
+LOCAL_MODULE_TAGS := tests
+LOCAL_CERTIFICATE := platform
+
+include $(BUILD_PACKAGE)