Throw TypeError if easing string is invalid.

third_party/WebKit/Source/core/animation/TimingInput.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef TimingInput_h
 #define TimingInput_h
 
 #include "core/CoreExport.h"
 #include "core/animation/Timing.h"
 #include "wtf/Allocator.h"
 
 namespace blink {
 
 class Dictionary;
+class ExceptionState;
 class KeyframeEffectOptions;
 
 class CORE_EXPORT TimingInput {
     STATIC_ONLY(TimingInput);
 public:
-    static Timing convert(const KeyframeEffectOptions& timingInput);
-    static Timing convert(double duration);
+    static bool convert(const KeyframeEffectOptions& timingInput, Timing& timingOutput, ExceptionState&);
+    static bool convert(double duration, Timing& timingOutput);

[alancutter (OOO until 2018), 2016/04/05 04:50:06]

Why does this need to change? It never returns false.

[suzyh_UTC10 (ex-contributor), 2016/04/12 08:04:23]

It doesn't _need_ to change, but as a user of this API I would expect the two
TimingInput::convert functions to be consistent in this regard.

[alancutter (OOO until 2018), 2016/04/13 00:46:38]

I think it makes the call sites harder to read. It's not clear why we're
asserting that it must succeed until you look into the definition.

[suzyh_UTC10 (ex-contributor), 2016/04/13 01:48:09]

OK, sure. I've put it back the way it was.

 
     static void setStartDelay(Timing&, double startDelay);
     static void setEndDelay(Timing&, double endDelay);
     static void setFillMode(Timing&, const String& fillMode);
     static void setIterationStart(Timing&, double iterationStart);
     static void setIterationCount(Timing&, double iterationCount);
     static void setIterationDuration(Timing&, double iterationDuration);
     static void setPlaybackRate(Timing&, double playbackRate);
     static void setPlaybackDirection(Timing&, const String& direction);
-    static void setTimingFunction(Timing&, const String& timingFunctionString);
+    static bool setTimingFunction(Timing&, const String& timingFunctionString, ExceptionState&);
 };
 
 } // namespace blink
 
 #endif