Throw TypeError if easing string is invalid.

third_party/WebKit/Source/core/frame/Deprecation.cpp

Index: third_party/WebKit/Source/core/frame/Deprecation.cpp
diff --git a/third_party/WebKit/Source/core/frame/Deprecation.cpp b/third_party/WebKit/Source/core/frame/Deprecation.cpp
index c55347d60e85ede6251e187715949af2fc148132..969408b58791065e1435b9adffe63c0b92a0d73a 100644
--- a/third_party/WebKit/Source/core/frame/Deprecation.cpp
+++ b/third_party/WebKit/Source/core/frame/Deprecation.cpp
@@ -370,6 +370,9 @@ String Deprecation::deprecationMessage(UseCounter::Feature feature)
     case UseCounter::TouchDragUserGestureUsedCrossOrigin:
         return willBeRemoved("Performing sensitive operations in iframes on touch events which don't represent a tap gesture", 52, "https://www.chromestatus.com/features/5649871251963904");
 
+    case UseCounter::WebAnimationsEasingAsFunctionLinear:
+        return String::format("Specifying animation easing as a function is deprecated and all support will be removed in %s, at which point this will throw a TypeError. This warning may have been triggered by the Web Animations or Polymer polyfills. See http://crbug.com/601672 for details.", milestoneString(54));
+
     // Features that aren't deprecated don't have a deprecation message.
     default:
         return String();