platform2: Explicitly use base:: namespace with CommandLine

The current revision of libchrome is removing CommandLine class
from global namespace and only retain the one in base::.

Sweep the code to use the correct namespace in anticpation of
libchrome revision roll.

BUG=None
TEST=./build_packages

Change-Id: Ib7ca448dac1204c1e36ab053e775a5a5214997ac
Reviewed-on: https://chromium-review.googlesource.com/263785
Trybot-Ready: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>

testrunner.cc

diff --git a/testrunner.cc b/testrunner.cc
index 139de75..6ca791e 100644
--- a/testrunner.cc
+++ b/testrunner.cc
@@ -29,7 +29,7 @@
   chromeos_update_engine::Terminator::Init(2);
   chromeos_update_engine::Subprocess::Init();
   LOG(INFO) << "parsing command line arguments";
-  CommandLine::Init(argc, argv);
+  base::CommandLine::Init(argc, argv);
   LOG(INFO) << "initializing gtest";
   ::testing::InitGoogleTest(&argc, argv);
   LOG(INFO) << "running unit tests";