Theme suppliers: Avoid all Image copying.

chrome/browser/themes/custom_theme_supplier.h

Index: chrome/browser/themes/custom_theme_supplier.h
diff --git a/chrome/browser/themes/custom_theme_supplier.h b/chrome/browser/themes/custom_theme_supplier.h
index cf4da937b08e78269e5378a2a77bc91aead18da2..f33275411a5ab1d65f6ca0f2dfd7b2cda9e9dde0 100644
--- a/chrome/browser/themes/custom_theme_supplier.h
+++ b/chrome/browser/themes/custom_theme_supplier.h
@@ -10,6 +10,7 @@
 #include "content/public/browser/browser_thread.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/base/layout.h"
+#include "ui/gfx/image/image.h"
 
 namespace base {
 class RefCountedMemory;
@@ -57,7 +58,7 @@ class CustomThemeSupplier : public base::RefCountedThreadSafe<
 
   // Returns the theme image for |id|. Returns an empty image if no image is
   // found for |id|.
-  virtual gfx::Image GetImageNamed(int id);
+  virtual const gfx::Image& GetImageNamed(int id);
 
   // Returns the raw PNG encoded data for IDR_THEME_NTP_*. This method only
   // works for the NTP attribution and background resources.
@@ -70,6 +71,8 @@ class CustomThemeSupplier : public base::RefCountedThreadSafe<
  protected:
   virtual ~CustomThemeSupplier();
 
+  const gfx::Image& empty_image() const { return empty_image_; }
+
  private:
   friend struct content::BrowserThread::DeleteOnThread<
       content::BrowserThread::FILE>;
@@ -77,6 +80,8 @@ class CustomThemeSupplier : public base::RefCountedThreadSafe<
 
   ThemeType theme_type_;
 
+  gfx::Image empty_image_;
+
   DISALLOW_COPY_AND_ASSIGN(CustomThemeSupplier);
 };