Add ability for Widgets to override the DefaultThemeProvider

ui/views/widget/widget.cc

Index: ui/views/widget/widget.cc
diff --git a/ui/views/widget/widget.cc b/ui/views/widget/widget.cc
index 154d107a63b298fbb7f6d0eb764d924ecc1a734b..7f120cf45a2f6408951a4ff0841735a816a50ac8 100644
--- a/ui/views/widget/widget.cc
+++ b/ui/views/widget/widget.cc
@@ -123,7 +123,8 @@ Widget::InitParams::InitParams()
       desktop_window_tree_host(NULL),
       layer_type(ui::LAYER_TEXTURED),
       context(NULL),
-      force_show_in_taskbar(false) {
+      force_show_in_taskbar(false),
+      theme_provider(nullptr) {
 }
 
 Widget::InitParams::InitParams(Type type)
@@ -146,7 +147,8 @@ Widget::InitParams::InitParams(Type type)
       desktop_window_tree_host(NULL),
       layer_type(ui::LAYER_TEXTURED),
       context(NULL),
-      force_show_in_taskbar(false) {
+      force_show_in_taskbar(false),
+      theme_provider(nullptr) {
 }
 
 Widget::InitParams::~InitParams() {
@@ -159,6 +161,7 @@ Widget::Widget()
     : native_widget_(NULL),
       widget_delegate_(NULL),
       non_client_view_(NULL),
+      theme_provider_(nullptr),
       dragged_view_(NULL),
       ownership_(InitParams::NATIVE_WIDGET_OWNS_WIDGET),
       is_secondary_widget_(true),
@@ -352,7 +355,10 @@ void Widget::Init(const InitParams& in_params) {
   native_widget_ = CreateNativeWidget(params.native_widget, this)->
                    AsNativeWidgetPrivate();
   root_view_.reset(CreateRootView());
-  default_theme_provider_.reset(new ui::DefaultThemeProvider);
+  if (in_params.theme_provider)
+    theme_provider_ = in_params.theme_provider;
+  else
+    default_theme_provider_.reset(new ui::DefaultThemeProvider);
   if (params.type == InitParams::TYPE_MENU) {
     is_mouse_button_pressed_ =
         internal::NativeWidgetPrivate::IsMouseButtonDown();
@@ -743,6 +749,8 @@ bool Widget::IsVisible() const {
 }
 
 ui::ThemeProvider* Widget::GetThemeProvider() const {
+  if (theme_provider_)
+    return theme_provider_;

[Peter Kasting, 2015/09/02 21:44:14]

It seems strange that we prefer root widget's default theme provider over our
own default theme provider, but we prefer our own non-default theme provider
over root widget's.

I think this is a symptom of fixing the problem the wrong way.  Instead of
setting an overriding theme provider on a child widget, shouldn't we be fixing
this problem by setting the correct (non-default) theme provider on the root
widgets for these various cases?  Then we wouldn't need to touch this function.

[jonross, 2015/09/02 22:02:26]

I had debated that approach, and am still open to it.

I wasn't sure if setting the ThemeProvider on the root widget would impact the
expectations of sibling widgets.

I also didn't want to litter the code with overrides of GetThemeProvider like
there are in BrowserFrame.

[jonross, 2015/09/09 14:54:36]

I've updated the change to only apply the desired ThemeProvider on the top level
widget.

   const Widget* root_widget = GetTopLevelWidget();
   if (root_widget && root_widget != this) {
     // Attempt to get the theme provider, and fall back to the default theme