Theme suppliers: Avoid all Image copying.

chrome/browser/ui/libgtk2ui/gtk2_ui.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/ui/libgtk2ui/gtk2_ui.h"
 
 #include <math.h>
 #include <pango/pango.h>
 #include <set>
 #include <utility>
@@ skipping 506 matching lines @@
 }
 
 void Gtk2UI::MaterialDesignControllerReady() {
   UpdateMaterialDesignColors();
 }
 
 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())
     return it->second;
 
   gfx::Image image = GenerateGtkThemeImage(id);
 
   if (image.IsEmpty()) {
     SkBitmap bitmap = GenerateGtkThemeBitmap(id);
     if (!bitmap.empty())
       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 {
   switch (id) {
     case ThemeProperties::TINT_BACKGROUND_TAB:
       // Tints for which the cross-platform default is fine. Before adding new
       // values here, specifically verify they work well on Linux.
       break;
     default:
       // Assume any tints not specifically verified on Linux aren't usable.
@@ skipping 837 matching lines @@
   // Blacklist scaling factors <130% (crbug.com/484400) and round
   // to 1 decimal to prevent rendering problems (crbug.com/485183).
   return scale < 1.3f ? 1.0f : roundf(scale * 10) / 10;
 }
 
 }  // namespace libgtk2ui
 
 views::LinuxUI* BuildGtk2UI() {
   return new libgtk2ui::Gtk2UI;
 }