Combine tab background image getter code into one place.

chrome/browser/ui/views/tabs/tab_strip.cc

Index: chrome/browser/ui/views/tabs/tab_strip.cc
diff --git a/chrome/browser/ui/views/tabs/tab_strip.cc b/chrome/browser/ui/views/tabs/tab_strip.cc
index da4e53b1304f7abbdabdb0ea84a35f3d9daaac67..5fe10f19ac6bb2a12ae82e7044e2b11bc1ccb845 100644
--- a/chrome/browser/ui/views/tabs/tab_strip.cc
+++ b/chrome/browser/ui/views/tabs/tab_strip.cc
@@ -398,11 +398,8 @@ void NewTabButton::PaintFill(bool pressed,
                              double hover_value,
                              float scale,
                              gfx::Canvas* canvas) const {
-  int bg_id = IDR_THEME_TAB_BACKGROUND_V;
-  if (!GetWidget()->ShouldWindowContentsBeTransparent()) {
-    bg_id = tab_strip_->controller()->IsIncognito() ?
-        IDR_THEME_TAB_BACKGROUND_INCOGNITO : IDR_THEME_TAB_BACKGROUND;
-  }
+  bool custom_image;
+  const int bg_id = tab_strip_->GetBackgroundResourceId(&custom_image);
 
   // Draw the fill background image.
   const gfx::Size size(GetNewTabButtonSize());
@@ -1208,6 +1205,28 @@ bool TabStrip::IsImmersiveStyle() const {
   return immersive_style_;
 }
 
+int TabStrip::GetBackgroundResourceId(bool* custom_image) const {
+  ui::ThemeProvider* theme_provider = GetThemeProvider();
+
+  if (GetWidget()->ShouldWindowContentsBeTransparent()) {
+    const int kBackgroundIdGlass = IDR_THEME_TAB_BACKGROUND_V;
+    *custom_image = theme_provider->HasCustomImage(kBackgroundIdGlass);
+    return kBackgroundIdGlass;
+  }
+
+  // If a custom theme does not provide a replacement tab background, but does
+  // provide a replacement frame image, HasCustomImage() on the tab background
+  // ID will return false, but the theme provider will make a custom image from
+  // the frame image.
+  const bool incognito = controller()->IsIncognito();
+  const int id = incognito ?
+      IDR_THEME_TAB_BACKGROUND_INCOGNITO : IDR_THEME_TAB_BACKGROUND;
+  *custom_image = theme_provider->HasCustomImage(id) ||
+      theme_provider->HasCustomImage(
+          incognito ? IDR_THEME_FRAME_INCOGNITO : IDR_THEME_FRAME);
+  return id;
+}
+
 void TabStrip::UpdateTabAccessibilityState(const Tab* tab,
                                            ui::AXViewState* state) {
   state->count = tab_count();