Web Animations API: Implement step-middle and steps(x, middle) timing functions.

Source/platform/animation/TimingFunctionTestHelper.h

-/*
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-
-/**
- * Make testing with gtest and gmock nicer by adding pretty print and other
- * helper functions.
- */
-
-#ifndef TimingFunctionTestHelper_h
-#define TimingFunctionTestHelper_h
-
-#include "platform/animation/TimingFunction.h"
-
-#include <ostream> // NOLINT
-
-namespace WebCore {
-
-void PrintTo(const TimingFunction&, ::std::ostream*);
-
-// operator== functions
-bool operator==(const LinearTimingFunction&, const TimingFunction&);
-bool operator==(const CubicBezierTimingFunction&, const TimingFunction&);
-bool operator==(const StepsTimingFunction&, const TimingFunction&);
-bool operator==(const ChainedTimingFunction&, const TimingFunction&);
-
-bool operator==(const TimingFunction&, const TimingFunction&);
-bool operator!=(const TimingFunction&, const TimingFunction&);
-
-} // namespace WebCore
-
-#endif