CC: Allow cubic-bezier timing inputs outside the range [0, 1]

ui/gfx/geometry/cubic_bezier.cc

 // Copyright 2014 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 "ui/gfx/geometry/cubic_bezier.h"
 
 #include <algorithm>
 #include <cmath>
 
 #include "base/logging.h"
@@ skipping 53 matching lines @@
   return t;
 }
 
 }  // namespace
 
 CubicBezier::CubicBezier(double x1, double y1, double x2, double y2)
     : x1_(x1),
       y1_(y1),
       x2_(x2),
       y2_(y2) {
+  InitGradients();
 }
 
 CubicBezier::~CubicBezier() {
 }
 
+void CubicBezier::InitGradients() {
+  if (x1_ > 0)
+    start_gradient_ = y1_ / x1_;
+  else if (!y1_ && x2_ > 0)
+    start_gradient_ = y2_ / x2_;
+  else
+    start_gradient_ = 0;
+
+  if (x2_ < 1)
+    end_gradient_ = (y2_ - 1) / (x2_ - 1);
+  else if (x2_ == 1 && x1_ < 1)
+    end_gradient_ = (y1_ - 1) / (x1_ - 1);
+  else
+    end_gradient_ = 0;
+}
+
 double CubicBezier::Solve(double x) const {
+  if (x < 0)
+    return start_gradient_ * x;
+  if (x > 1)
+    return 1.0 + end_gradient_ * (x - 1.0);
+
   return eval_bezier(y1_, y2_, bezier_interp(x1_, x2_, x));
 }
 
 double CubicBezier::Slope(double x) const {
   double t = bezier_interp(x1_, x2_, x);
   double dx_dt = eval_bezier_derivative(x1_, x2_, t);
   double dy_dt = eval_bezier_derivative(y1_, y2_, t);
   return dy_dt / dx_dt;
 }
 
@@ skipping 40 matching lines @@
     sol_1 = eval_bezier(y1_, y2_, t_1);
 
   if (0 < t_2 && t_2 < 1)
     sol_2 = eval_bezier(y1_, y2_, t_2);
 
   *min = std::min(std::min(*min, sol_1), sol_2);
   *max = std::max(std::max(*max, sol_1), sol_2);
 }
 
 }  // namespace gfx