Move GetNewTabCSS() caching off the startup path.

chrome/browser/ui/webui/theme_source.h

Index: chrome/browser/ui/webui/theme_source.h
diff --git a/chrome/browser/ui/webui/theme_source.h b/chrome/browser/ui/webui/theme_source.h
index 22aee4be146291b8e608dd93bee84e991678ddd7..be1f7274b68b2557729ab4037c7079c3508a3e5d 100644
--- a/chrome/browser/ui/webui/theme_source.h
+++ b/chrome/browser/ui/webui/theme_source.h
@@ -33,7 +33,6 @@ class ThemeSource : public content::URLDataSource {
   std::string GetMimeType(const std::string& path) const override;
   base::MessageLoop* MessageLoopForRequestPath(
       const std::string& path) const override;
-  bool ShouldReplaceExistingSource() const override;
   bool ShouldServiceRequest(const net::URLRequest* request) const override;
 
  private:
@@ -49,12 +48,9 @@ class ThemeSource : public content::URLDataSource {
                       int resource_id,
                       float scale);
 
-  // The original profile (never an OTR profile).
+  // The profile this object was initialized with.
   Profile* profile_;
 
-  // We grab the CSS early so we don't have to go back to the UI thread later.
-  scoped_refptr<base::RefCountedMemory> css_bytes_;
-
   DISALLOW_COPY_AND_ASSIGN(ThemeSource);
 };