Use "linear" as the default easing for neutral keyframes in element.animate()

third_party/WebKit/Source/core/animation/EffectInput.cpp

Index: third_party/WebKit/Source/core/animation/EffectInput.cpp
diff --git a/third_party/WebKit/Source/core/animation/EffectInput.cpp b/third_party/WebKit/Source/core/animation/EffectInput.cpp
index 0df3f2f9202ac787f0102f647698e06e9dcda4ac..1f4e5224412a1f48b6153ee493517a3f8fb4f428 100644
--- a/third_party/WebKit/Source/core/animation/EffectInput.cpp
+++ b/third_party/WebKit/Source/core/animation/EffectInput.cpp
@@ -104,7 +104,7 @@ EffectModel* createEffectModelFromKeyframes(Element& element, const StringKeyfra
     if (encounteredCompositableProperty && element.inActiveDocument())
         element.document().updateLayoutTreeForNode(&element);
 
-    StringKeyframeEffectModel* keyframeEffectModel = StringKeyframeEffectModel::create(keyframes);
+    StringKeyframeEffectModel* keyframeEffectModel = StringKeyframeEffectModel::create(keyframes, LinearTimingFunction::shared());
     if (!RuntimeEnabledFeatures::cssAdditiveAnimationsEnabled()) {
         for (const auto& keyframeGroup : keyframeEffectModel->getPropertySpecificKeyframeGroups()) {
             PropertyHandle property = keyframeGroup.key;