Move default tag from libbase to liblog

Bug: 119867234
Test: log tags look right, libbase/liblog unit tests
Change-Id: I3670c3fdce3d0238a23a53bba2877ffed1291f9c
diff --git a/liblog/tests/Android.bp b/liblog/tests/Android.bp
index 3288954..b3364f9 100644
--- a/liblog/tests/Android.bp
+++ b/liblog/tests/Android.bp
@@ -54,6 +54,7 @@
     ],
     srcs: [
         "libc_test.cpp",
+        "liblog_default_tag.cpp",
         "liblog_global_state.cpp",
         "liblog_test.cpp",
         "log_id_test.cpp",