Linux Aura: Use managed tab dragging when possible (Reland)

chrome/browser/ui/views/tabs/tab_drag_controller.cc

 // Copyright (c) 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 "chrome/browser/ui/views/tabs/tab_drag_controller.h"
 
 #include <math.h>
 #include <set>
 
 #include "base/auto_reset.h"
@@ skipping 361 matching lines @@
 
     // On windows SaveFocus() may trigger a capture lost, which destroys us.
     {
       base::WeakPtr<TabDragController> ref(weak_factory_.GetWeakPtr());
       SaveFocus();
       if (!ref)
         return;
     }
     started_drag_ = true;
     Attach(source_tabstrip_, gfx::Point());
+    gfx::Point drag_point_in_screen = point_in_screen;
     if (static_cast<int>(drag_data_.size()) ==
         GetModel(source_tabstrip_)->count()) {
       if (was_source_maximized_ || was_source_fullscreen_) {
         did_restore_window_ = true;
         // When all tabs in a maximized browser are dragged the browser gets
         // restored during the drag and maximized back when the drag ends.
         views::Widget* widget = GetAttachedBrowserWidget();
         const int last_tabstrip_width = attached_tabstrip_->GetTabAreaWidth();
         std::vector<gfx::Rect> drag_bounds = CalculateBoundsForDraggedTabs();
         OffsetX(GetAttachedDragPoint(point_in_screen).x(), &drag_bounds);
         gfx::Rect new_bounds(CalculateDraggedBrowserBounds(source_tabstrip_,
                                                            point_in_screen,
                                                            &drag_bounds));
         new_bounds.Offset(-widget->GetRestoredBounds().x() +
                           point_in_screen.x() -
                           mouse_offset_.x(), 0);
         widget->SetVisibilityChangedAnimationsEnabled(false);
         widget->Restore();
         widget->SetBounds(new_bounds);
         AdjustBrowserAndTabBoundsForDrag(last_tabstrip_width,
                                          point_in_screen,
                                          &drag_bounds);
         widget->SetVisibilityChangedAnimationsEnabled(true);
       } else {
+#if !defined(OS_LINUX) || defined(OS_CHROMEOS)
         // The user has to move the mouse some amount of pixels before the drag
         // starts. Offset the window by this amount so that the relative offset
         // of the initial location is consistent. See crbug.com/518740
         views::Widget* widget = GetAttachedBrowserWidget();
         gfx::Rect bounds = widget->GetWindowBoundsInScreen();
         bounds.Offset(point_in_screen.x() - start_point_in_screen_.x(),
                       point_in_screen.y() - start_point_in_screen_.y());
         widget->SetBounds(bounds);
+#else
+        // Linux does not need the window offset behavior above because all drag
+        // implementations move windows relative to a passed-in cursor position
+        // instead of the implicit current cursor position like on Windows.
+        drag_point_in_screen = start_point_in_screen_;
+#endif
       }
-      RunMoveLoop(GetWindowOffset(point_in_screen));
+      RunMoveLoop(GetWindowOffset(drag_point_in_screen));
       return;
     }
   }
 
   if (ContinueDragging(point_in_screen) == Liveness::DELETED)
     return;
 }
 
 void TabDragController::EndDrag(EndDragReason reason) {
   TRACE_EVENT0("views", "TabDragController::EndDrag");
@@ skipping 1412 matching lines @@
   // TODO(pkotwicz): Fix this properly (crbug.com/358482)
   for (auto* browser : *BrowserList::GetInstance()) {
     if (browser->tab_strip_model()->empty())
       exclude.insert(browser->window()->GetNativeWindow());
   }
 #endif
   base::WeakPtr<TabDragController> ref(weak_factory_.GetWeakPtr());
   *window = window_finder_->GetLocalProcessWindowAtPoint(screen_point, exclude);
   return ref ? Liveness::ALIVE : Liveness::DELETED;
 }