Only load theme images for the scale factors that use them

chrome/browser/themes/browser_theme_pack.h

Index: chrome/browser/themes/browser_theme_pack.h
diff --git a/chrome/browser/themes/browser_theme_pack.h b/chrome/browser/themes/browser_theme_pack.h
index 8eca0b402abdc0d49db676e329e965a263151066..e66a388c1d5d2e662a68b14179ca05e57c355793 100644
--- a/chrome/browser/themes/browser_theme_pack.h
+++ b/chrome/browser/themes/browser_theme_pack.h
@@ -90,6 +90,13 @@ class BrowserThemePack : public base::RefCountedThreadSafe<
   base::RefCountedMemory* GetRawData(int id,
                                      ui::ScaleFactor scale_factor) const;
 
+  // Returns the raw PNG encoded data for IDR_THEME_NTP_* for the available
+  // scale factor with the highest scale if available, otherwise NULL.
+  // The corresponding scale factor is returned in |scale_factor|.
+  base::RefCountedMemory* GetRawDataWithHighestScale(
+      int id,
+      ui::ScaleFactor* scale_factor) const;
+
   // Returns the set of image idrs which can be overwritten by a user provided
   // theme.
   static void GetThemeableImageIDRs(std::set<int>* result);
@@ -267,6 +274,9 @@ class BrowserThemePack : public base::RefCountedThreadSafe<
   // The scale factors represented by the images in the theme pack.
   std::vector<ui::ScaleFactor> scale_factors_;
 
+  // The scale factors ordered by scale from lowest to highest.
+  std::vector<ui::ScaleFactor> scale_factors_ordered_by_scale_;
+
   // References to raw PNG data. This map isn't touched when |data_pack_| is
   // non-NULL; |image_memory_| is only filled during BuildFromExtension(). Any
   // image data that needs to be written to the DataPack during WriteToDisk()
@@ -284,6 +294,8 @@ class BrowserThemePack : public base::RefCountedThreadSafe<
   // or vice versa.
   ImageCache images_on_file_thread_;
 
+  base::WeakPtrFactory<BrowserThemePack> weak_ptr_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(BrowserThemePack);
 };