ui: Remove use of bitmaps when painting tab backgrounds.

ui/gfx/scoped_canvas.h

Index: ui/gfx/scoped_canvas.h
diff --git a/ui/gfx/scoped_canvas.h b/ui/gfx/scoped_canvas.h
index 96ccaffa25d3a28c1f6d4b0295b5224afeeed224..c4c7014475c6f8569f47958a64435ec5864c4957 100644
--- a/ui/gfx/scoped_canvas.h
+++ b/ui/gfx/scoped_canvas.h
@@ -23,6 +23,18 @@ class GFX_EXPORT ScopedCanvas {
       canvas_->Restore();
   }
 
+  ScopedCanvas(ScopedCanvas&& o) {

[Peter Kasting, 2017/04/06 00:52:11]

Nit: Per Google style guide constructors and assignment operator all go above
destructor

[danakj, 2017/04/06 17:05:28]

I didn't realize this, thanks.
https://google.github.io/styleguide/cppguide.html#Declaration_Order

Removed these for now though.

+    canvas_ = o.canvas_;
+    o.canvas_ = nullptr;
+  }
+  ScopedCanvas& operator=(ScopedCanvas&& o) {
+    if (canvas_)
+      canvas_->Restore();
+    canvas_ = o.canvas_;
+    o.canvas_ = nullptr;
+    return *this;
+  }
+
  private:
   gfx::Canvas* canvas_;