ui/gfx: Make gfx::Canvas inherit from gfx::CanvasSkia.

ui/views/controls/button/text_button.cc

Index: ui/views/controls/button/text_button.cc
diff --git a/ui/views/controls/button/text_button.cc b/ui/views/controls/button/text_button.cc
index 13861b8bf108dd41236ba6bb47e9fac4517270d4..504adef75cb021064b4a50d30bc188dbb6da4974 100644
--- a/ui/views/controls/button/text_button.cc
+++ b/ui/views/controls/button/text_button.cc
@@ -516,7 +516,7 @@ void TextButtonBase::PaintButton(gfx::Canvas* canvas, PaintButtonMode mode) {
 #if defined(OS_WIN)
       // TODO(erg): Either port DrawStringWithHalo to linux or find an
       // alternative here.
-      canvas->AsCanvasSkia()->DrawStringWithHalo(
+      canvas->DrawStringWithHalo(
           text_, font_, text_color, color_highlight_, text_bounds.x(),
           text_bounds.y(), text_bounds.width(), text_bounds.height(),
           draw_string_flags);
@@ -531,7 +531,7 @@ void TextButtonBase::PaintButton(gfx::Canvas* canvas, PaintButtonMode mode) {
                             draw_string_flags);
 #endif
     } else if (has_text_halo_) {
-      canvas->AsCanvasSkia()->DrawStringWithHalo(
+      canvas->DrawStringWithHalo(
           text_, font_, text_color, text_halo_color_,
           text_bounds.x(), text_bounds.y(), text_bounds.width(),
           text_bounds.height(), draw_string_flags);