Bug 1336891 - stylo: Implement custom property value getter. r=emilio

MozReview-Commit-ID: AfAJtNJyCSO

--HG--
extra : rebase_source : 04a5fa6f2fb7b86f67c225156d08b1bf56348ea3

layout/style/ServoBindingList.h

@@ -545,6 +545,11 @@ SERVO_BINDING_FUNC(Servo_SerializeFontValueForCanvas, void,
                    RawServoDeclarationBlockBorrowed declarations,
                    nsAString* buffer)
 
+// Get custom property value.
+SERVO_BINDING_FUNC(Servo_GetCustomProperty, bool,
+                   ServoComputedValuesBorrowed computed_values,
+                   const nsAString* name, nsAString* value)
+
 // Style-struct management.
 #define STYLE_STRUCT(name, checkdata_cb)                            \
   struct nsStyle##name;                                             \

layout/style/nsComputedDOMStyle.cpp

@@ -6913,12 +6913,14 @@ nsComputedDOMStyle::DoGetCustomProperty(const nsAString& aPropertyName)
 {
   MOZ_ASSERT(nsCSSProps::IsCustomPropertyName(aPropertyName));
 
-  const nsStyleVariables* variables = StyleVariables();
-
   nsString variableValue;
   const nsAString& name = Substring(aPropertyName,
                                     CSS_CUSTOM_NAME_PREFIX_LENGTH);
-  if (!variables->mVariables.Get(name, variableValue)) {
+  bool present = mStyleContext->IsServo()
+    ? Servo_GetCustomProperty(mStyleContext->ComputedValues(),
+                              &name, &variableValue)
+    : StyleVariables()->mVariables.Get(name, variableValue);
+  if (!present) {
     return nullptr;
   }