Add support for calculating the position of the top controls in the cc layer.

cc/top_controls_animation.cc

Index: cc/top_controls_animation.cc
diff --git a/cc/top_controls_animation.cc b/cc/top_controls_animation.cc
new file mode 100644
index 0000000000000000000000000000000000000000..7720533f0efa7636715b785e618e06024a1b20ad
--- /dev/null
+++ b/cc/top_controls_animation.cc
@@ -0,0 +1,59 @@
+// 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/top_controls_animation.h"
+
+#include "base/logging.h"
+#include "cc/timing_function.h"
+
+using base::TimeDelta;
+using base::TimeTicks;
+
+namespace cc {
+
+scoped_ptr<TopControlsAnimation> TopControlsAnimation::Create(
+    float start_y_offset,
+    float top_controls_height,
+    TimeTicks start_time,
+    TimeDelta max_duration) {
+  return make_scoped_ptr(new TopControlsAnimation(
+      start_y_offset, top_controls_height, start_time, max_duration));
+}
+
+TopControlsAnimation::TopControlsAnimation(float start_y_offset,
+                                           float top_controls_height,
+                                           TimeTicks start_time,
+                                           TimeDelta max_duration)
+    : start_y_offset_(start_y_offset),
+      top_controls_height_(top_controls_height),
+      direction_(1),
+      start_time_(start_time),
+      max_duration_(max_duration) {
+  timing_function_ = EaseTimingFunction::create();
+}
+
+TopControlsAnimation::~TopControlsAnimation() {
+}
+
+void TopControlsAnimation::SetDirection(bool showing) {
+  direction_ = showing ? 1 : -1;
+}
+
+float TopControlsAnimation::ScrollOffsetAtTime(TimeTicks time) const {
+  TimeDelta elapsed_time = time - start_time_;
+  float offset_delta = timing_function_->getValue(
+      elapsed_time.InSecondsF() / max_duration_.InSecondsF())
+          * direction_ * top_controls_height_;
+  return start_y_offset_ + offset_delta;
+}
+
+bool TopControlsAnimation::IsAnimationCompleteAtTime(TimeTicks time) const {
+  float scroll_offset = ScrollOffsetAtTime(time);
+  if (direction_ == 1)
+    return scroll_offset >= 0;
+  else
+    return scroll_offset <= -top_controls_height_;
+}
+
+}  // namespace cc