Remove requirement that mojo::Environment be instantiated.

mojo/public/cpp/environment/tests/logging_unittest.cc

Index: mojo/public/cpp/environment/tests/logging_unittest.cc
diff --git a/mojo/public/cpp/environment/tests/logging_unittest.cc b/mojo/public/cpp/environment/tests/logging_unittest.cc
index ab1de6450966ee8312fc07487740c27421e3bb89..e3af7aae55ed9449f56b72456f4acd0738c24285 100644
--- a/mojo/public/cpp/environment/tests/logging_unittest.cc
+++ b/mojo/public/cpp/environment/tests/logging_unittest.cc
@@ -30,7 +30,8 @@ bool DcheckTestHelper(bool* was_called) {
 
 class LoggingTest : public testing::Test {
  public:
-  LoggingTest() : environment_(nullptr, &kMockLogger) {
+  LoggingTest() {
+    Environment::SetDefaultLogger(&kMockLogger);
     minimum_log_level_ = MOJO_LOG_LEVEL_INFO;
     ResetMockLogger();
   }
@@ -82,8 +83,6 @@ class LoggingTest : public testing::Test {
     minimum_log_level_ = minimum_log_level;
   }
 
-  Environment environment_;
-
   static const MojoLogger kMockLogger;
   static MojoLogLevel minimum_log_level_;
   static bool log_message_was_called_;