Gtk3: Render a GtkHeaderBar as the background of the tab strip

ui/views/window/frame_background.h

Index: ui/views/window/frame_background.h
diff --git a/ui/views/window/frame_background.h b/ui/views/window/frame_background.h
index a420de556cf1e8e1643d6e67b3bbe3677e0e25e4..2dc80cb9b8a67ceed5e52967b3b63e5e89e504d7 100644
--- a/ui/views/window/frame_background.h
+++ b/ui/views/window/frame_background.h
@@ -29,6 +29,9 @@ class VIEWS_EXPORT FrameBackground {
   // Sets the color to draw under the frame images.
   void set_frame_color(SkColor color) { frame_color_ = color; }
 
+  // Sets whether the frame to be drawn should have focus.

[Peter Kasting, 2017/01/12 18:53:53]

Nit: This sounds as if the frame will be given focus.  Maybe "Distinguishes
between active (foreground) and inactive (background) window frame styles", or
something.

[Tom (Use chromium acct), 2017/01/12 21:51:10]

Done.

+  void set_is_active(bool is_active) { is_active_ = is_active; }
+
   // Sets the theme image for the top of the window.  May be null (empty).
   // Memory is owned by the caller.
   void set_theme_image(const gfx::ImageSkia& image) { theme_image_ = image; }
@@ -74,7 +77,11 @@ class VIEWS_EXPORT FrameBackground {
   // Fills the frame area with the frame color.
   void PaintFrameColor(gfx::Canvas* canvas, const View* view) const;
 
+  // Paints the background of the tab strip.
+  void PaintFrameTopArea(gfx::Canvas* canvas, const View* view) const;
+
   SkColor frame_color_;
+  bool is_active_;
   gfx::ImageSkia theme_image_;
   gfx::ImageSkia theme_overlay_image_;
   int top_area_height_;