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/vision/blob/threshold_test.cc b/aos/vision/blob/threshold_test.cc
index 67f7116..4b23f3e 100644
--- a/aos/vision/blob/threshold_test.cc
+++ b/aos/vision/blob/threshold_test.cc
@@ -9,9 +9,7 @@
 #include "aos/vision/blob/range_image.h"
 #include "aos/vision/image/image_types.h"
 
-namespace aos {
-namespace vision {
-namespace testing {
+namespace aos::vision::testing {
 
 class YuyvYThresholdTest : public ::testing::Test {
  public:
@@ -189,6 +187,4 @@
   }
 }
 
-}  // namespace testing
-}  // namespace vision
-}  // namespace aos
+}  // namespace aos::vision::testing