cros: Fix wallpaper manager indexing vector out-of-range issue

chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc

Index: chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc
diff --git a/chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc b/chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc
index 29a0a38524e9d718f543ed5daa3464b23409e089..7b01d15668ac392604ae410c77589ed6f9d81e4f 100644
--- a/chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc
+++ b/chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc
@@ -950,7 +950,7 @@ void WallpaperManager::OnWindowDestroying(aura::Window* window) {
 void WallpaperManager::OnColorCalculationComplete() {
   size_t num_of_calculation = color_calculator_->prominent_colors().size();
   DCHECK_EQ(1u, num_of_calculation);
-  SkColor color = color_calculator_->prominent_colors()[num_of_calculation];
+  SkColor color = color_calculator_->prominent_colors()[num_of_calculation - 1];
   color_calculator_->RemoveObserver(this);
   color_calculator_.reset();
   if (prominent_color_ == color)