Bug 1392447 - Fix up Servo_StyleSheet_GetOrigin for Linux 32-bit ABI. r=emilio

Bindgen bitfield enums don't work as return values with the Linux 32-bit ABI at
the moment because they wrap the value in a struct.

This causes the Rust side to believe the caller will pass along space for the
struct return value, while C++ believes it's just an integer value.

MozReview-Commit-ID: JHDp0XAmQCG

layout/style/ServoBindingList.h

@@ -55,8 +55,10 @@ SERVO_BINDING_FUNC(Servo_StyleSheet_Clone, RawServoStyleSheetContentsStrong,
 SERVO_BINDING_FUNC(Servo_StyleSheet_SizeOfIncludingThis, size_t,
                    mozilla::MallocSizeOf malloc_size_of,
                    RawServoStyleSheetContentsBorrowed sheet)
-SERVO_BINDING_FUNC(Servo_StyleSheet_GetOrigin,
-                   mozilla::OriginFlags,
+// We'd like to return `OriginFlags` here, but bindgen bitfield enums don't
+// work as return values with the Linux 32-bit ABI at the moment because
+// they wrap the value in a struct.
+SERVO_BINDING_FUNC(Servo_StyleSheet_GetOrigin, uint8_t,
                    RawServoStyleSheetContentsBorrowed sheet)
 SERVO_BINDING_FUNC(Servo_StyleSet_Init, RawServoStyleSet*, RawGeckoPresContextOwned pres_context)
 SERVO_BINDING_FUNC(Servo_StyleSet_RebuildCachedData, void,

layout/style/ServoStyleSheet.cpp

@@ -466,7 +466,8 @@ ServoStyleSheet::SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const
 OriginFlags
 ServoStyleSheet::GetOrigin()
 {
-  return Servo_StyleSheet_GetOrigin(Inner()->mContents);
+  return static_cast<OriginFlags>(
+    Servo_StyleSheet_GetOrigin(Inner()->mContents));
 }
 
 } // namespace mozilla