Mojo Log service and a thread-safe client library.

mojo/public/cpp/environment/lib/environment.cc

Index: mojo/public/cpp/environment/lib/environment.cc
diff --git a/mojo/public/cpp/environment/lib/environment.cc b/mojo/public/cpp/environment/lib/environment.cc
index 6fb7e22a2204ef57185897050d743391b5a1684a..b5214718323bcbf927aeb01301cf54accc5c53ed 100644
--- a/mojo/public/cpp/environment/lib/environment.cc
+++ b/mojo/public/cpp/environment/lib/environment.cc
@@ -23,6 +23,7 @@ void Init(const MojoAsyncWaiter* default_async_waiter,
   g_default_async_waiter = default_async_waiter
                                ? default_async_waiter
                                : &internal::kDefaultAsyncWaiter;
+
   g_default_logger =
       default_logger ? default_logger : &internal::kDefaultLogger;
 
@@ -62,6 +63,13 @@ const MojoLogger* Environment::GetDefaultLogger() {
 }
 
 // static
+void Environment::SetDefaultLogger(const MojoLogger* logger) {
+  assert(g_default_logger);  // Fails if not "inside" |Environment|.
+  assert(logger);
+  g_default_logger = logger;
+}
+
+// static
 void Environment::InstantiateDefaultRunLoop() {
   assert(!RunLoop::current());
   // Not leaked: accessible from |RunLoop::current()|.