Brushes up the code of screenshot filename.

ash/accelerators/accelerator_controller.cc

Index: ash/accelerators/accelerator_controller.cc
diff --git a/ash/accelerators/accelerator_controller.cc b/ash/accelerators/accelerator_controller.cc
index f5598a2b42bd95412f72dbeb0452cb45e4e6fded..0383ef74b2d7169c73cf5c9772fc7ac0fb9ce41b 100644
--- a/ash/accelerators/accelerator_controller.cc
+++ b/ash/accelerators/accelerator_controller.cc
@@ -440,11 +440,8 @@ bool AcceleratorController::PerformAction(int action,
     case TAKE_SCREENSHOT:
     case TAKE_SCREENSHOT_BY_PRTSCN_KEY:
       if (screenshot_delegate_.get() &&
-          screenshot_delegate_->CanTakeScreenshot()) {
-        Shell::RootWindowList root_windows = Shell::GetAllRootWindows();
-        for (size_t i = 0; i < root_windows.size(); ++i)
-          screenshot_delegate_->HandleTakeScreenshot(root_windows[i]);
-      }
+          screenshot_delegate_->CanTakeScreenshot())
+        screenshot_delegate_->HandleTakeScreenshotForAllRootWindows();
       // Return true to prevent propagation of the key event.
       return true;
     case TAKE_PARTIAL_SCREENSHOT: