Combine tab background image getter code into one place.

chrome/browser/ui/views/tabs/tab_controller.h

Index: chrome/browser/ui/views/tabs/tab_controller.h
diff --git a/chrome/browser/ui/views/tabs/tab_controller.h b/chrome/browser/ui/views/tabs/tab_controller.h
index 23de0380f145b6534e55a7aac4e55498bdfe502d..f8485e076699415564fd27eba21596bde403c9eb 100644
--- a/chrome/browser/ui/views/tabs/tab_controller.h
+++ b/chrome/browser/ui/views/tabs/tab_controller.h
@@ -96,6 +96,11 @@ class TabController {
   // Returns true if tabs painted in the rectangular light-bar style.
   virtual bool IsImmersiveStyle() const = 0;
 
+  // Returns the resource ID for the image to use as the tab background.
+  // |custom_image| is an outparam set to true if either the tab or the frame
+  // background images have been customized; see implementation comments.
+  virtual int GetBackgroundResourceId(bool* custom_image) const = 0;
+
   // Adds private information to the tab's accessibility state.
   virtual void UpdateTabAccessibilityState(const Tab* tab,
                                         ui::AXViewState* state) = 0;