Theme suppliers: Avoid all Image copying.

chrome/browser/ui/libgtk2ui/gtk2_ui.cc

Index: chrome/browser/ui/libgtk2ui/gtk2_ui.cc
diff --git a/chrome/browser/ui/libgtk2ui/gtk2_ui.cc b/chrome/browser/ui/libgtk2ui/gtk2_ui.cc
index 433fc9d4d83d0bfde30aa3cfcb4774426a32410d..f1a55e5e788ac9e36c6b91cb08e041501a067580 100644
--- a/chrome/browser/ui/libgtk2ui/gtk2_ui.cc
+++ b/chrome/browser/ui/libgtk2ui/gtk2_ui.cc
@@ -524,7 +524,7 @@ Gtk2UI::~Gtk2UI() {
   ClearAllThemeData();
 }
 
-gfx::Image Gtk2UI::GetThemeImageNamed(int id) const {
+const gfx::Image& Gtk2UI::GetThemeImageNamed(int id) const {
   // Try to get our cached version:
   ImageCache::const_iterator it = gtk_images_.find(id);
   if (it != gtk_images_.end())
@@ -538,8 +538,8 @@ gfx::Image Gtk2UI::GetThemeImageNamed(int id) const {
       image = gfx::Image::CreateFrom1xBitmap(bitmap);
   }
 
-  gtk_images_[id] = image;
-  return image;
+  auto result = gtk_images_.insert(std::make_pair(id, image));
+  return result.first->second;
 }
 
 bool Gtk2UI::GetTint(int id, color_utils::HSL* tint) const {