Use float/PointF for window dragging code

This will make window dragging in tablet mode smoother.

I'll convert splitview code in a separate CL.

Bug:1031927
Test: manually tested on slate.

Change-Id: I99f28c6239e31cbd8556ce9e5fd18a01fab50b18
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1987580
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#729867}

• ash/home_screen/drag_window_from_shelf_controller.cc[diff]
• ash/shelf/shelf_window_watcher_unittest.cc[diff]
• ash/wm/default_window_resizer.cc[diff]
• ash/wm/default_window_resizer.h[diff]
• ash/wm/default_window_resizer_unittest.cc[diff]
• ash/wm/drag_details.cc[diff]
• ash/wm/drag_details.h[diff]
• ash/wm/drag_window_resizer.cc[diff]
• ash/wm/drag_window_resizer.h[diff]
• ash/wm/drag_window_resizer_unittest.cc[diff]
• ash/wm/mru_window_tracker_unittest.cc[diff]
• ash/wm/overview/overview_controller_unittest.cc[diff]
• ash/wm/overview/overview_session_unittest.cc[diff]
• ash/wm/pip/pip_window_resizer.cc[diff]
• ash/wm/pip/pip_window_resizer.h[diff]
• ash/wm/pip/pip_window_resizer_unittest.cc[diff]
• ash/wm/splitview/split_view_controller.cc[diff]
• ash/wm/splitview/split_view_controller_unittest.cc[diff]
• ash/wm/tablet_mode/tablet_mode_browser_window_drag_delegate.cc[diff]
• ash/wm/tablet_mode/tablet_mode_browser_window_drag_delegate.h[diff]
• ash/wm/tablet_mode/tablet_mode_controller_unittest.cc[diff]
• ash/wm/tablet_mode/tablet_mode_window_drag_delegate.cc[diff]
• ash/wm/tablet_mode/tablet_mode_window_drag_delegate.h[diff]
• ash/wm/tablet_mode/tablet_mode_window_resizer.cc[diff]
• ash/wm/tablet_mode/tablet_mode_window_resizer.h[diff]
• ash/wm/toplevel_window_event_handler.cc[diff]
• ash/wm/toplevel_window_event_handler.h[diff]
• ash/wm/window_resizer.cc[diff]
• ash/wm/window_resizer.h[diff]
• ash/wm/window_state.cc[diff]
• ash/wm/window_state.h[diff]
• ash/wm/window_state_delegate.h[diff]
• ash/wm/workspace/multi_window_resize_controller.cc[diff]
• ash/wm/workspace/multi_window_resize_controller.h[diff]
• ash/wm/workspace/multi_window_resize_controller_unittest.cc[diff]
• ash/wm/workspace/workspace_window_resizer.cc[diff]
• ash/wm/workspace/workspace_window_resizer.h[diff]
• ash/wm/workspace/workspace_window_resizer_unittest.cc[diff]
• ash/wm/workspace_controller_unittest.cc[diff]
• components/exo/client_controlled_shell_surface.cc[diff]
• components/exo/client_controlled_shell_surface.h[diff]
• components/exo/client_controlled_shell_surface_unittest.cc[diff]
• components/exo/shell_surface.cc[diff]
• components/exo/wayland/zcr_remote_shell.cc[diff]