Add/Remove mmap tests.

Remove the incorrect tests that use a negative offset for mmap without
a fd.

Add a small set of tests for mmap.

Bug: 15436969

Change-Id: Id537d33cd4cdc26dee6cdfa9bf9cf35754bce335

tests/TemporaryFile.h

@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#include <fcntl.h>
 #include <unistd.h>
 
 template<int (*mk_fn)(char*)>
@@ -39,6 +40,11 @@ class GenericTemporaryFile {
     unlink(filename);
   }
 
+  void reopen() {
+    close(fd);
+    fd = open(filename, O_RDWR);
+  }
+
   int fd;
   char filename[1024];