Adding momentum/overscroll to views:: ScrollViews

ui/compositor/overscroll/ui_scroll_input_manager.cc

+// Copyright 2016 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/compositor/overscroll/ui_scroll_input_manager.h"
+
+#include "base/logging.h"
+#include "ui/compositor/overscroll/ui_input_handler.h"
+#include "ui/events/event.h"
+
+namespace ui {
+
+UIScrollInputManager::UIScrollInputManager(
+    const base::WeakPtr<cc::InputHandler>& input_handler)
+    : input_wrapper_(new UIInputHandler(input_handler)) {}
+
+UIScrollInputManager::~UIScrollInputManager() {}
+
+void UIScrollInputManager::OnScrollEvent(const ScrollEvent& event) {
+  // On Mac, an event ending the non-fling portion of a scroll can't be
+  // distinguished from an event ending a scroll that won't fling. The start of
+  // the fling is therefore made identifiable by being an an update only (not a
+  // "begin"). But since the InputHandler has already been told of the end,
+  // treat the first momentum fling as a "resume" by holding state.
+  if (!scrolling_) {
+    scrolling_ = true;
+    input_wrapper_->HandleScrollBegin(event);
+  }
+  input_wrapper_->HandleScrollUpdate(event);
+  if (event.momentum_phase() & EM_PHASE_END) {
+    DCHECK(scrolling_);
+    scrolling_ = false;
+    input_wrapper_->HandleScrollEnd(event);
+  }
+}
+
+}  // namespace ui