Make callers of CommandLine use it via the base:: namespace.

chrome/browser/prefetch/prefetch_browsertest.cc

Index: chrome/browser/prefetch/prefetch_browsertest.cc
diff --git a/chrome/browser/prefetch/prefetch_browsertest.cc b/chrome/browser/prefetch/prefetch_browsertest.cc
index cd3b57e796b94a2271d695057cc66b5fb909d12d..9ff446fc5e234fb753bdeb855f134b7c110889af 100644
--- a/chrome/browser/prefetch/prefetch_browsertest.cc
+++ b/chrome/browser/prefetch/prefetch_browsertest.cc
@@ -49,7 +49,7 @@ class PrefetchBrowserTestBase : public InProcessBrowserTest {
   explicit PrefetchBrowserTestBase(bool disabled_via_field_trial)
       : disabled_via_field_trial_(disabled_via_field_trial) {}
 
-  void SetUpCommandLine(CommandLine* command_line) override {
+  void SetUpCommandLine(base::CommandLine* command_line) override {
     if (disabled_via_field_trial_) {
       command_line->AppendSwitchASCII(switches::kForceFieldTrials,
                                       "Prefetch/ExperimentDisabled/");