adb: make adb_basename match the POSIX behavior.

Previously, adb_basename was behaving according to the GNU, POSIX-incompatible
basename, despite POSIX adb_dirname existing alongside it. This patch changes
adb_basename to pass through to the POSIX basename.

Bug: http://b/25456821
Change-Id: I62a4865cccf3b9cdbc112e3e53ff475aa4a23bd9
diff --git a/adb_utils_test.cpp b/adb_utils_test.cpp
index 4a2787a..93c20cb 100644
--- a/adb_utils_test.cpp
+++ b/adb_utils_test.cpp
@@ -102,6 +102,13 @@
 TEST(adb_utils, adb_basename) {
   EXPECT_EQ("sh", adb_basename("/system/bin/sh"));
   EXPECT_EQ("sh", adb_basename("sh"));
+  EXPECT_EQ("sh", adb_basename("/system/bin/sh/"));
+}
+
+TEST(adb_utils, adb_dirname) {
+  EXPECT_EQ("/system/bin", adb_dirname("/system/bin/sh"));
+  EXPECT_EQ(".", adb_dirname("sh"));
+  EXPECT_EQ("/system/bin", adb_dirname("/system/bin/sh/"));
 }
 
 TEST(adb_utils, parse_host_and_port) {