Mojo: Add logging macros (and supporting code) for use in mojo/public/cpp.

mojo/mojo_public.gypi

 {
   'targets': [
     {
       'target_name': 'mojo_system',
       'type': 'static_library',
       'defines': [
         'MOJO_SYSTEM_IMPLEMENTATION',
       ],
       'include_dirs': [
         '..',
@@ skipping 144 matching lines @@
         '../base/base.gyp:base',
         '../testing/gtest.gyp:gtest',
         'mojo_environment_standalone',
         'mojo_public_test_utils',
         'mojo_run_all_unittests',
         'mojo_utility',
       ],
       'sources': [
         'public/cpp/environment/tests/async_waiter_unittest.cc',
         'public/cpp/environment/tests/logger_unittest.cc',
+        'public/cpp/environment/tests/logging_unittest.cc',
       ],
     },
     {
       'target_name': 'mojo_public_system_unittests',
       'type': 'executable',
       'dependencies': [
         '../base/base.gyp:base',
         '../testing/gtest.gyp:gtest',
         'mojo_cpp_bindings',
         'mojo_public_test_utils',
@@ skipping 138 matching lines @@
       'dependencies': [
         'mojo_cpp_bindings',
       ],
     },
     {
       'target_name': 'mojo_environment_standalone',
       'type': 'static_library',
       'sources': [
         'public/c/environment/async_waiter.h',
         'public/c/environment/logger.h',
+        'public/c/environment/logging.h',
         'public/cpp/environment/environment.h',
         'public/cpp/environment/lib/default_async_waiter.cc',
         'public/cpp/environment/lib/default_async_waiter.h',
         'public/cpp/environment/lib/default_logger.cc',
         'public/cpp/environment/lib/default_logger.h',
         'public/cpp/environment/lib/environment.cc',
+        'public/cpp/environment/lib/logging.cc',
       ],
       'include_dirs': [
         '..',
       ],
     },
     {
       'target_name': 'mojo_utility',
       'type': 'static_library',
       'sources': [
         'public/cpp/utility/mutex.h',
@@ skipping 91 matching lines @@
           },
           'dependencies': [
             'mojo_public_java',
           ],
           'includes': [ '../build/java.gypi' ],
         },
       ],
     }],
   ],
 }