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/ImageDataSerializer.cpp

@@ -44,7 +44,7 @@ struct SurfaceBufferInfo
     return GetAlignedStride<16>(sizeof(SurfaceBufferInfo));
   }
 };
-} // anonymous namespace
+} // namespace
 
 static SurfaceBufferInfo*
 GetBufferInfo(uint8_t* aData, size_t aDataSize)