Remove NullValue() from CalculateTransformedProgress

NullValue() is represented as a NaN in a double. We could better return
a base::Optional<double> and use the undefined base::Optional as null
value. Also there is no need for the IsNull() call as we could just use
the returned value as a boolean.

Bug: 994811
Change-Id: Ibb4a6b89102dd49450d68aae35b03e9eba46332f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1760963Reviewed-by: Kevin Ellis <kevers@chromium.org>
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Commit-Queue: Sergio Villar <svillar@igalia.com>
Cr-Commit-Position: refs/heads/master@{#689101}

third_party/blink/renderer/core/animation/timing.cc

@@ -181,9 +181,6 @@ Timing::CalculatedTiming Timing::CalculateTimings(
   progress = CalculateTransformedProgress(
       current_phase, directed_progress, iteration_duration,
       current_direction_is_forwards, timing_function);
-  if (IsNull(progress.value())) {
-    progress.reset();
-  }
 
   double time_to_next_iteration = std::numeric_limits<double>::infinity();
   // Conditionally compute the time to next iteration, which is only

third_party/blink/renderer/core/animation/timing_calculations.h

@@ -261,14 +261,14 @@ static inline double CalculateDirectedProgress(
 }
 
 // https://drafts.csswg.org/web-animations/#calculating-the-transformed-progress
-static inline double CalculateTransformedProgress(
+static inline base::Optional<double> CalculateTransformedProgress(
     Timing::Phase phase,
     double directed_progress,
     double iteration_duration,
     bool is_current_direction_forward,
     scoped_refptr<TimingFunction> timing_function) {
   if (IsNull(directed_progress))
-    return NullValue();
+    return base::nullopt;
 
   // Set the before flag to indicate if at the leading edge of an iteration.
   // This is used to determine if the left or right limit should be used if at a

third_party/blink/renderer/core/animation/timing_calculations_test.cc

@@ -324,8 +324,8 @@ TEST(AnimationTimingCalculationsTest, TransformedProgress) {
       StepsTimingFunction::Create(4, StepsTimingFunction::StepPosition::END);
 
   // directed_progress is null.
-  EXPECT_TRUE(IsNull(CalculateTransformedProgress(
-      Timing::kPhaseActive, NullValue(), 1, true, timing_function)));
+  EXPECT_FALSE(CalculateTransformedProgress(Timing::kPhaseActive, NullValue(),
+                                            1, true, timing_function));
 
   // At step boundaries.
   // Forward direction.