Move C++ mu_guard class out of C-core public headers and fix style.
diff --git a/gRPC-C++.podspec b/gRPC-C++.podspec
index 1d3cedb..ae3bd4b 100644
--- a/gRPC-C++.podspec
+++ b/gRPC-C++.podspec
@@ -236,6 +236,7 @@
                       'src/core/lib/gprpp/fork.h',
                       'src/core/lib/gprpp/manual_constructor.h',
                       'src/core/lib/gprpp/memory.h',
+                      'src/core/lib/gprpp/mutex_lock.h',
                       'src/core/lib/gprpp/thd.h',
                       'src/core/lib/profiling/timers.h',
                       'src/core/ext/transport/chttp2/transport/bin_decoder.h',
@@ -534,6 +535,7 @@
                               'src/core/lib/gprpp/fork.h',
                               'src/core/lib/gprpp/manual_constructor.h',
                               'src/core/lib/gprpp/memory.h',
+                              'src/core/lib/gprpp/mutex_lock.h',
                               'src/core/lib/gprpp/thd.h',
                               'src/core/lib/profiling/timers.h',
                               'src/core/lib/avl/avl.h',