Move ReadFileToString to the base namespace.

tools/android/device_stats_monitor/device_stats_monitor.cc

Index: tools/android/device_stats_monitor/device_stats_monitor.cc
diff --git a/tools/android/device_stats_monitor/device_stats_monitor.cc b/tools/android/device_stats_monitor/device_stats_monitor.cc
index 6388cdaf4365f153a383fb3a13e5120ceeedeffd..ef2fee9d9e09de2cb61ba1e9e067bd7b7685b86a 100644
--- a/tools/android/device_stats_monitor/device_stats_monitor.cc
+++ b/tools/android/device_stats_monitor/device_stats_monitor.cc
@@ -44,8 +44,8 @@ class DeviceStatsMonitor {
     std::string out;
     while (record_) {
       out.clear();
-      CHECK(file_util::ReadFileToString(io_stats_path, &out));
-      CHECK(file_util::ReadFileToString(cpu_stats_path, &out));
+      CHECK(base::ReadFileToString(io_stats_path, &out));
+      CHECK(base::ReadFileToString(cpu_stats_path, &out));
       samples_.push_back(out);
       usleep(sample_interval);
     }