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 280969a84e5e7d0067d1f10378dec9d6d15061fb..71df4501d12ffa4d44c3426e4afb6e0281ad3c6e 100644
--- a/ui/views/widget/widget.cc
+++ b/ui/views/widget/widget.cc
@@ -122,7 +122,8 @@ 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)
@@ -145,7 +146,8 @@ 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() {
@@ -158,6 +160,7 @@ 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),
@@ -351,7 +354,10 @@ 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();
@@ -742,6 +748,8 @@ bool Widget::IsVisible() const {
 }
 
 ui::ThemeProvider* Widget::GetThemeProvider() const {
+  if (theme_provider_)
+    return theme_provider_;
   const Widget* root_widget = GetTopLevelWidget();
   if (root_widget && root_widget != this) {
     // Attempt to get the theme provider, and fall back to the default theme