Tweaks the pinned background tab title change animation per Nicholas's

app/multi_animation.cc

 // Copyright (c) 2010 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 "app/multi_animation.h"
 
 // Default interval, in ms.
 static const int kDefaultInterval = 20;
 
 static int TotalTime(const MultiAnimation::Parts& parts) {
   int time_ms = 0;
-  for (size_t i = 0; i < parts.size(); ++i)
+  for (size_t i = 0; i < parts.size(); ++i) {
+    DCHECK(parts[i].end_time_ms - parts[i].start_time_ms >= parts[i].time_ms);
     time_ms += parts[i].time_ms;
+  }
   return time_ms;
 }
 
 MultiAnimation::MultiAnimation(const Parts& parts)
     : Animation(base::TimeDelta::FromMilliseconds(kDefaultInterval)),
       parts_(parts),
       cycle_time_ms_(TotalTime(parts)),
       current_value_(0),
       current_part_index_(0) {
   DCHECK(!parts_.empty());
 }
 
 void MultiAnimation::Step(base::TimeTicks time_now) {
   double last_value = current_value_;
   size_t last_index = current_part_index_;
 
   int delta = static_cast<int>((time_now - start_time()).InMilliseconds() %
                                cycle_time_ms_);
   const Part& part = GetPart(&delta, &current_part_index_);
-  double percent = static_cast<double>(delta) /
-        static_cast<double>(part.time_ms);
+  double percent = static_cast<double>(delta + part.start_time_ms) /
+        static_cast<double>(part.end_time_ms);
+  DCHECK(percent <= 1);
   current_value_ = Tween::CalculateValue(part.type, percent);
 
   if ((current_value_ != last_value || current_part_index_ != last_index) &&
       delegate()) {
     delegate()->AnimationProgressed(this);
   }
 }
 
 const MultiAnimation::Part& MultiAnimation::GetPart(int* time_ms,
                                                     size_t* part_index) {
   DCHECK(*time_ms < cycle_time_ms_);
 
   for (size_t i = 0; i < parts_.size(); ++i) {
     if (*time_ms < parts_[i].time_ms) {
       *part_index = i;
       return parts_[i];
     }
 
     *time_ms -= parts_[i].time_ms;
   }
   NOTREACHED();
   *time_ms = 0;
   *part_index = 0;
   return parts_[0];
 }