Bug 845188; initialise CommonAnimationData::mGenerationCount; r=roc

layout/style/AnimationCommon.h

@@ -135,6 +135,7 @@ struct CommonElementAnimationData : public PRCList
     : mElement(aElement)
     , mElementProperty(aElementProperty)
     , mManager(aManager)
+    , mAnimationGeneration(0)
 #ifdef DEBUG
     , mCalledPropertyDtor(false)
 #endif