style: Add CssPropFlags::SerializedByServo and use it on some simple …

…properties.

The idea is to turn the simple properties into a blacklist instead really soon,
and fix the offending ones soon after, so that only shorthands and properties
with layout dependence (and maybe the scrollbar properties, because the poke at
LookAndFeel) are not serialized by Servo.

Bug: 1467536
Reviewed-by: xidorn
MozReview-Commit-ID: JTLNnmXzny8

components/style/properties/data.py

@@ -226,6 +226,10 @@ def __init__(self, style_struct, name, spec=None, animation_value_type=None, key
         # See compute_damage for the various values this can take
         self.servo_restyle_damage = servo_restyle_damage
 
+    @staticmethod
+    def type():
+        return "longhand"
+
     def experimental(self, product):
         if product == "gecko":
             return bool(self.gecko_pref)
@@ -361,6 +365,10 @@ def get_transitionable(self):
     animatable = property(get_animatable)
     transitionable = property(get_transitionable)
 
+    @staticmethod
+    def type():
+        return "shorthand"
+
     def experimental(self, product):
         if product == "gecko":
             return bool(self.gecko_pref)
@@ -392,6 +400,10 @@ def __init__(self, name, original, gecko_pref):
         self.allowed_in_page_rule = original.allowed_in_page_rule
         self.allowed_in_keyframe_block = original.allowed_in_keyframe_block
 
+    @staticmethod
+    def type():
+        return "alias"
+
     def experimental(self, product):
         if product == "gecko":
             return bool(self.gecko_pref)