CC: Support fractional iteration count on compositor animations

cc/animation/animation.cc

 // Copyright 2012 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.
 
 #include "cc/animation/animation.h"
 
 #include <cmath>
 
 #include "base/debug/trace_event.h"
 #include "base/strings/string_util.h"
@@ skipping 176 matching lines @@
     return 0;
 
   // check if we are past active interval
   bool is_past_total_duration =
       (iterations_ > 0 &&
        trimmed_in_seconds >= curve_->Duration() * iterations_);
 
   // We need to know the current iteration if we're alternating.
   int iteration = 0;
 
-  // If we are past the active interval, return iteration duration.
+  // If we are past the active interval, return iteration duration of last
+  // iteration
   if (is_past_total_duration) {
     iteration = iterations_ - 1;
-    trimmed_in_seconds = curve_->Duration();
+    double frac = fmod(curve_->Duration() * iterations_, curve_->Duration());
+    trimmed_in_seconds = frac == 0 ? curve_->Duration() : frac;
   } else {
     iteration = static_cast<int>(trimmed_in_seconds / curve_->Duration());
     // Calculate x where trimmed = x + n * curve_->Duration() for some positive
     // integer n.
     trimmed_in_seconds = fmod(trimmed_in_seconds, curve_->Duration());
   }
 
   // check if we are running the animation in reverse direction for the current
   // iteration
   bool reverse = (direction_ == Reverse) ||
@@ skipping 28 matching lines @@
   // the main thread.
   if (run_state_ == Animation::Paused ||
       other->run_state_ == Animation::Paused) {
     other->run_state_ = run_state_;
     other->pause_time_ = pause_time_;
     other->total_paused_time_ = total_paused_time_;
   }
 }
 
 }  // namespace cc