Bug 1382077 part 3 - Record viewport unit usage and generate proper restyle hint. r=heycam

MozReview-Commit-ID: FA2TiIejUT

--HG--
extra : rebase_source : f34741f4129c669aff3588c17bb81f5feca29e67

layout/style/ServoBindingList.h

@@ -47,8 +47,8 @@ SERVO_BINDING_FUNC(Servo_StyleSet_Clear, void,
                    RawServoStyleSetBorrowed set)
 SERVO_BINDING_FUNC(Servo_StyleSet_RebuildData, void,
                    RawServoStyleSetBorrowed set)
-SERVO_BINDING_FUNC(Servo_StyleSet_MediumFeaturesChanged, bool,
-                   RawServoStyleSetBorrowed set)
+SERVO_BINDING_FUNC(Servo_StyleSet_MediumFeaturesChanged, nsRestyleHint,
+                   RawServoStyleSetBorrowed set, bool viewport_changed)
 SERVO_BINDING_FUNC(Servo_StyleSet_Drop, void, RawServoStyleSetOwned set)
 SERVO_BINDING_FUNC(Servo_StyleSet_CompatModeChanged, void,
                    RawServoStyleSetBorrowed raw_data)

layout/style/ServoStyleSet.cpp

@@ -116,17 +116,7 @@ ServoStyleSet::InvalidateStyleForCSSRuleChanges()
 nsRestyleHint
 ServoStyleSet::MediumFeaturesChanged(bool aViewportChanged) const
 {
-  if (Servo_StyleSet_MediumFeaturesChanged(mRawSet.get())) {
-    return eRestyle_Subtree;
-  }
-  if (aViewportChanged) {
-    // Rebuild all style data without rerunning selector matching.
-    //
-    // FIXME(emilio, bug 1328652): We don't set mUsesViewportUnits in stylo yet,
-    // so assume the worst.
-    return eRestyle_ForceDescendants;
-  }
-  return nsRestyleHint(0);
+  return Servo_StyleSet_MediumFeaturesChanged(mRawSet.get(), aViewportChanged);
 }
 
 size_t