Add basic tests for ashmem

Test: CL only adds tests. Ran them to confirm they pass.
Change-Id: Iccc3edaeeabff27f23b3786c3d40b2eb5b02dc83
Signed-off-by: Connor O'Brien <connoro@google.com>
diff --git a/libcutils/tests/Android.bp b/libcutils/tests/Android.bp
index ada7d5f..06d0e28 100644
--- a/libcutils/tests/Android.bp
+++ b/libcutils/tests/Android.bp
@@ -19,6 +19,7 @@
     target: {
         android: {
             srcs: [
+                "AshmemTest.cpp",
                 "MemsetTest.cpp",
                 "PropertiesTest.cpp",
                 "sched_policy_test.cpp",