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

Source/platform/animation/TimingFunctionTestHelper.cpp

Index: Source/platform/animation/TimingFunctionTestHelper.cpp
diff --git a/Source/platform/animation/TimingFunctionTestHelper.cpp b/Source/platform/animation/TimingFunctionTestHelper.cpp
index 74e74aea8cdba7660160d90d7cc77a3a7f6abeaa..26a5df16ff90cf0c715f5ff8ecadb02507655eb9 100644
--- a/Source/platform/animation/TimingFunctionTestHelper.cpp
+++ b/Source/platform/animation/TimingFunctionTestHelper.cpp
@@ -134,6 +134,9 @@ void PrintTo(const StepsTimingFunction& timingFunction, ::std::ostream* os)
     case StepsTimingFunction::Start:
         *os << "Start";
         break;
+    case StepsTimingFunction::Middle:
+        *os << "Middle";
+        break;
     case StepsTimingFunction::End:
         *os << "End";
         break;
@@ -144,7 +147,21 @@ void PrintTo(const StepsTimingFunction& timingFunction, ::std::ostream* os)
         ASSERT_NOT_REACHED();
     }
     *os << ", " << timingFunction.numberOfSteps();
-    *os << ", " << (timingFunction.stepAtStart() ? "true" : "false");
+    *os << ", ";
+
+    switch (timingFunction.stepAtPosition()) {
+    case StepsTimingFunction::StepAtStart:
+        *os << "StepAtStart";
+        break;
+    case StepsTimingFunction::StepAtMiddle:
+        *os << "StepAtMiddle";
+        break;
+    case StepsTimingFunction::StepAtEnd:
+        *os << "StepAtEnd";
+        break;
+    default:
+        ASSERT_NOT_REACHED();
+    }
     *os << ")";
 }
 
@@ -207,7 +224,7 @@ bool operator==(const StepsTimingFunction& lhs, const TimingFunction& rhs)
 
     const StepsTimingFunction& stf = toStepsTimingFunction(rhs);
     if ((lhs.subType() == StepsTimingFunction::Custom) && (stf.subType() == StepsTimingFunction::Custom))
-        return (lhs.numberOfSteps() == stf.numberOfSteps()) && (lhs.stepAtStart() == stf.stepAtStart());
+        return (lhs.numberOfSteps() == stf.numberOfSteps()) && (lhs.stepAtPosition() == stf.stepAtPosition());
 
     return lhs.subType() == stf.subType();
 }