Bug 1182996 - Fix and add missing namespace comments. rs=ehsan

The bulk of this commit was generated by running:

  run-clang-tidy.py \
    -checks='-*,llvm-namespace-comment' \
    -header-filter=^/.../mozilla-central/.* \
    -fix

gfx/layers/basic/MacIOSurfaceTextureHostBasic.cpp

@@ -93,5 +93,5 @@ MacIOSurfaceTextureHostBasic::GetSize() const {
                       mSurface->GetDevicePixelHeight());
 }
 
-}
-}
+} // namespace layers
+} // namespace mozilla