Prefix CommandLine usage with base namespace (Part 4: ash/)

Prefix all CommandLine usage in the ash/ directory with the
base:: namespace.

BUG=422426

Review URL: https://codereview.chromium.org/684783004

Cr-Commit-Position: refs/heads/master@{#301819}
diff --git a/ash/root_window_controller_unittest.cc b/ash/root_window_controller_unittest.cc
index 28999b6..dd80b41f 100644
--- a/ash/root_window_controller_unittest.cc
+++ b/ash/root_window_controller_unittest.cc
@@ -612,7 +612,7 @@
   ~VirtualKeyboardRootWindowControllerTest() override {}
 
   void SetUp() override {
-    CommandLine::ForCurrentProcess()->AppendSwitch(
+    base::CommandLine::ForCurrentProcess()->AppendSwitch(
         keyboard::switches::kEnableVirtualKeyboard);
     test::AshTestBase::SetUp();
     Shell::GetPrimaryRootWindowController()->ActivateKeyboard(