Move C++ mu_guard class out of C-core public headers and fix style.
diff --git a/package.xml b/package.xml
index 76bdd5a..c89d490 100644
--- a/package.xml
+++ b/package.xml
@@ -110,6 +110,7 @@
     <file baseinstalldir="/" name="src/core/lib/gprpp/fork.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/gprpp/manual_constructor.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/gprpp/memory.h" role="src" />
+    <file baseinstalldir="/" name="src/core/lib/gprpp/mutex_lock.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/gprpp/thd.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/profiling/timers.h" role="src" />
     <file baseinstalldir="/" name="src/core/lib/gpr/alloc.cc" role="src" />