Bug 1278430 - Update the first keyframe value as well as property value when replacing transition. r=birtles

MozReview-Commit-ID: teNZdJdKoy

--HG--
extra : rebase_source : 88589ef8cea26e86c43eb9fa4c403a3cad17f09b

layout/style/nsTransitionManager.cpp

@@ -105,6 +105,18 @@ ElementPropertyTransition::UpdateStartValueFromReplacedTransition()
                  mProperties[0].mSegments.Length() == 1,
                  "The transition should have one property and one segment");
       mProperties[0].mSegments[0].mFromValue = Move(startValue);
+      nsCSSValue cssValue;
+      DebugOnly<bool> uncomputeResult =
+        StyleAnimationValue::UncomputeValue(mProperties[0].mProperty,
+                                            startValue,
+                                            cssValue);
+      MOZ_ASSERT(uncomputeResult, "UncomputeValue should not fail");
+      MOZ_ASSERT(mKeyframes.Length() == 2,
+          "Transitions should have exactly two animation keyframes");
+      MOZ_ASSERT(mKeyframes[0].mPropertyValues.Length() == 1,
+          "Transitions should have exactly one property in their first "
+          "frame");
+      mKeyframes[0].mPropertyValues[0].mValue = cssValue;
     }
   }
 

layout/style/test/file_transitions_replacement_on_busy_frame.html

@@ -47,7 +47,8 @@ window.addEventListener("load", function() {
 
   // Wait for a paint to ensure that the first transition has started.
   waitForAllPaints(function() {
-    var previousMatrix;
+    var previousPropertyValue;
+    var previousKeyframeValue;
     var anim;
     requestAnimationFrame(function() {
       // Start second transition
@@ -56,7 +57,8 @@ window.addEventListener("load", function() {
 
       anim = div.getAnimations()[0];
       var properties = SpecialPowers.wrap(anim.effect).getProperties();
-      previousMatrix = properties[0].values[0].value;
+      previousPropertyValue = properties[0].values[0].value;
+      previousKeyframeValue = anim.effect.getKeyframes()[0].transform;
     });
 
     requestAnimationFrame(function() {
@@ -73,10 +75,13 @@ window.addEventListener("load", function() {
       // process that we update the transition start point).
       waitForAllPaints(function() {
         var properties = SpecialPowers.wrap(anim.effect).getProperties();
-        var currentMatrix = properties[0].values[0].value;
-        isnot(currentMatrix, previousMatrix,
+        var currentPropertyValue = properties[0].values[0].value;
+        isnot(currentPropertyValue, previousPropertyValue,
               "From value of transition is updated since the moment when " +
               "it was generated");
+        isnot(anim.effect.getKeyframes()[0].transform, previousKeyframeValue,
+              "Keyframe value of transition is updated since the moment when " +
+              "it was generated");
         finish();
       });
     });