Nest all namespaces

The compiler supports this now.  We can type less going forward.
No functional changes.

Signed-off-by: Stephan Pleines <pleines.stephan@gmail.com>
Change-Id: I29d6fa4f9aacc0e381f1a7637294db0392466995
diff --git a/aos/testing/gtest_main.cc b/aos/testing/gtest_main.cc
index 2fb77fe..6071bde 100644
--- a/aos/testing/gtest_main.cc
+++ b/aos/testing/gtest_main.cc
@@ -14,16 +14,13 @@
 DEFINE_string(log_file, "",
               "Print all log messages to FILE instead of standard output.");
 
-namespace aos {
-
-namespace testing {
+namespace aos::testing {
 
 // Actually declared/defined in //aos/testing:test_logging.
 void SetLogFileName(const char *filename) __attribute__((weak));
 void ForcePrintLogsDuringTests() __attribute__((weak));
 
-}  // namespace testing
-}  // namespace aos
+}  // namespace aos::testing
 
 GTEST_API_ int main(int argc, char **argv) {
   ::testing::InitGoogleTest(&argc, argv);