Bug 1749390 - Add debug support for mozilla::Side. r=gfx-reviewers,lsalzman

This was useful so may as well land it. Need to use mozilla::Side in the
header because otherwise it is ambiguous with mozilla::ipc::Side, yay
C++.

Depends on D135562

Differential Revision: https://phabricator.services.mozilla.com/D135563

gfx/2d/Types.cpp

@@ -11,6 +11,28 @@
 #include <ostream>
 
 namespace mozilla {
+
+std::ostream& operator<<(std::ostream& aOut, const Side& aSide) {
+#define Emit(x) \
+  case x:       \
+    aOut << #x; \
+    break
+
+  switch (aSide) {
+    Emit(eSideTop);
+    Emit(eSideBottom);
+    Emit(eSideLeft);
+    Emit(eSideRight);
+    default:
+      NS_ERROR("unknown side");
+      aOut << int(aSide);
+      break;
+  }
+
+#undef Emit
+  return aOut;
+}
+
 namespace gfx {
 
 std::ostream& operator<<(std::ostream& aOut, const SurfaceFormat& aFormat) {

gfx/2d/Types.h

@@ -858,6 +858,8 @@ namespace mozilla {
 // Side constants for use in various places.
 enum Side : uint8_t { eSideTop, eSideRight, eSideBottom, eSideLeft };
 
+std::ostream& operator<<(std::ostream&, const mozilla::Side&);
+
 constexpr auto AllPhysicalSides() {
   return mozilla::MakeInclusiveEnumeratedRange(eSideTop, eSideLeft);
 }