Issue #1769 - Part 2 Follow-up: Do not use namespace parent::child {} for defining nested namespaces.

It doesn't build for MSVC on Windows. Also other decoders are using the old
 way for defining nested namespaces, so better be consistent here.

image/DecoderFactory.h

@@ -15,7 +15,8 @@
 #include "nsCOMPtr.h"
 #include "SurfaceFlags.h"
 
-namespace mozilla::image {
+namespace mozilla {
+namespace image {
 
 class Decoder;
 class IDecodingTask;
@@ -200,6 +201,7 @@ private:
                                               bool aIsRedecode);
 };
 
-} // namespace mozilla::image
+} // namespace image
+} // namespace mozilla
 
 #endif // mozilla_image_DecoderFactory_h

image/decoders/nsJXLDecoder.cpp

@@ -17,7 +17,8 @@
 
 using namespace mozilla::gfx;
 
-namespace mozilla::image {
+namespace mozilla {
+namespace image {
 
 #define JXL_TRY(expr)                        \
   do {                                       \
@@ -162,4 +163,5 @@ nsJXLDecoder::FinishedJXLData()
   return Transition::TerminateFailure();
 }
 
-}  // namespace mozilla::image
+}  // namespace image
+}  // namespace mozilla

image/decoders/nsJXLDecoder.h

@@ -13,7 +13,8 @@
 #include "jxl/decode_cxx.h"
 #include "jxl/thread_parallel_runner_cxx.h"
 
-namespace mozilla::image {
+namespace mozilla {
+namespace image {
 class RasterImage;
 
 class nsJXLDecoder final : public Decoder {
@@ -45,6 +46,7 @@ class nsJXLDecoder final : public Decoder {
   JxlBasicInfo mInfo{};
 };
 
-}  // namespace mozilla::image
+}  // namespace image
+}  // namespace mozilla
 
 #endif  // mozilla_image_decoders_nsJXLDecoder_h