* src/window.c (window_body_height): Add WINDOW_TAB_LINE_HEIGHT.
(Fwindow_tab_line_height): New function.
(coordinates_in_window): Use window_wants_tab_line with
CURRENT_TAB_LINE_HEIGHT.
(window_relative_x_coord): Add ON_TAB_LINE.
(Fcoordinates_in_window_p): Add ON_TAB_LINE.
(window_from_coordinates): Add new arg tab_bar_p.
(Fwindow_line_height): Use window_wants_tab_line with
WINDOW_TAB_LINE_HEIGHT.
(Fwindow_lines_pixel_dimensions): Add WINDOW_TAB_LINE_HEIGHT.
(make_window): Set tab_line_height to -1.
(window_wants_tab_line): New function.
(window_internal_height): Use window_wants_tab_line.
(window_scroll_pixel_based): Add WINDOW_TAB_LINE_HEIGHT.
(Frecenter): Set minimize_tab_bar_window_p to 1.
(GCALIGNED_STRUCT): Add frame_tab_bar_lines and frame_tab_bar_height.
(Fcurrent_window_configuration): Set frame_tab_bar_lines and
frame_tab_bar_height.
(set_window_scroll_bars): Add WINDOW_TAB_LINE_HEIGHT.
(syms_of_window): Add Qtab_line_format and Swindow_tab_line_height.
* src/xdisp.c (window_box_height): Add window_wants_tab_line with
MATRIX_TAB_LINE_ROW and CURRENT_TAB_LINE_HEIGHT.
(pos_visible_p): Use window_wants_tab_line.
Add WINDOW_TAB_LINE_HEIGHT.
(get_glyph_string_clip_rects): Add WINDOW_TAB_LINE_HEIGHT.
(get_phys_cursor_geometry): Add WINDOW_TAB_LINE_HEIGHT.
(remember_mouse_glyph): Use MATRIX_TAB_LINE_ROW for part
ON_TAB_LINE.
(init_iterator): Use MATRIX_TAB_LINE_ROW for TAB_LINE_FACE_ID.
Add WINDOW_TAB_LINE_HEIGHT. Add window_wants_tab_line.
(Fwindow_text_pixel_size): Add WINDOW_TAB_LINE_HEIGHT.
(prepare_menu_bars): Call update_tab_bar.
(update_tab_bar, build_desired_tab_bar_string)
(display_tab_bar_line, tab_bar_height, Ftab_bar_height)
(redisplay_tab_bar, tab_bar_item_info, get_tab_bar_item)
(handle_tab_bar_click, note_tab_bar_highlight): New functions.
(compute_window_start_on_continuation_line): Use window_wants_tab_line.
(try_cursor_movement): Use window_wants_tab_line with
CURRENT_TAB_LINE_HEIGHT.
(redisplay_window): Use window_wants_tab_line with
CURRENT_TAB_LINE_HEIGHT.
(try_window_reusing_current_matrix): Use window_wants_tab_line
with WINDOW_TAB_LINE_HEIGHT.
(Fdump_tab_bar_row): New function.
(compute_line_metrics): Add WINDOW_TAB_LINE_HEIGHT.
(display_line): Use window_wants_tab_line.
(display_mode_line): Set tab_line_p to true if face_id is
TAB_LINE_FACE_ID.
(Fformat_mode_line): Handle Qtab_line and Qtab_bar.
(gui_clear_end_of_line): Add WINDOW_TAB_LINE_HEIGHT.
(erase_phys_cursor): Use WINDOW_TAB_LINE_HEIGHT.
(show_mouse_face): Use tab_bar_window.
(note_mode_line_or_margin_highlight): Use MATRIX_TAB_LINE_ROW for
area ON_TAB_LINE.
(note_mouse_highlight): Call note_tab_bar_highlight,
(expose_frame): Handle tab_bar_window.
(syms_of_xdisp): Add Sdump_tab_bar_row and Stab_bar_height.
(auto-resize-tab-bars, auto-raise-tab-bar-buttons)
(tab-bar-border, tab-bar-button-margin, tab-bar-button-relief)
(tab-bar-max-label-size): New variables.
* src/xfaces.c (lookup_basic_face): Add TAB_LINE_FACE_ID and
TAB_BAR_FACE_ID.
(syms_of_xfaces): Define Qtab_bar and Qtab_line.
* src/xfns.c (x_set_tab_bar_lines, x_change_tab_bar_height):
New functions.
(xic_set_statusarea): Add FRAME_TABBAR_TOP_HEIGHT.
(frame_geometry): Add FRAME_TAB_BAR_HEIGHT and Qtab_bar_size.
* src/xterm.c (x_draw_image_relief): Use tab_bar_button_relief.
(x_draw_image_relief): Use TAB_BAR_FACE_ID.
(handle_one_xevent): Handle tab_bar_window.
(x_set_window_size_1): Add FRAME_TABBAR_WIDTH.
(x_create_terminal): Set change_tab_bar_height_hook.