Add design doc link to SampledEffect::WillNeverChange()

Change-Id: I8616c8b57f7cd04475bd720760d5f71a1ba3b849
Reviewed-on: https://chromium-review.googlesource.com/874973Reviewed-by: Eric Willigers <ericwilligers@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Commit-Queue: Eric Willigers <ericwilligers@chromium.org>
Cr-Commit-Position: refs/heads/master@{#530413}

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

@@ -16,6 +16,8 @@ void SampledEffect::Clear() {
   interpolations_.clear();
 }
 
+// Design doc:
+// https://docs.google.com/document/d/1NomOWRrGQHlynQGO64CgdqRPAAEHhi3fSa8sf0Ip6xE
 bool SampledEffect::WillNeverChange() const {
   return !effect_ || !effect_->GetAnimation();
 }