GTK: First draft of using native themes, partially based on evan's CL 118358.

chrome/browser/profile.h

Index: chrome/browser/profile.h
diff --git a/chrome/browser/profile.h b/chrome/browser/profile.h
index 7190cc75447c4319ce123d1412550b7dec377fab..302d222a70d0e132a3c5fbd8107845ec8b09945f 100644
--- a/chrome/browser/profile.h
+++ b/chrome/browser/profile.h
@@ -188,6 +188,9 @@ class Profile {
   // Set the theme to the specified extension.
   virtual void SetTheme(Extension* extension) = 0;
 
+  // Set the theme to the machine's native theme.
+  virtual void SetNativeTheme() = 0;
+
   // Clear the theme and reset it to default.
   virtual void ClearTheme() = 0;
 
@@ -340,6 +343,7 @@ class ProfileImpl : public Profile,
   virtual DownloadManager* GetDownloadManager();
   virtual void InitThemes();
   virtual void SetTheme(Extension* extension);
+  virtual void SetNativeTheme();
   virtual void ClearTheme();
   virtual ThemeProvider* GetThemeProvider();
   virtual ThumbnailStore* GetThumbnailStore();