[Cleanup] Remove StringPrintf from global namespace

ash/system/monitor/tray_monitor.cc

Index: ash/system/monitor/tray_monitor.cc
diff --git a/ash/system/monitor/tray_monitor.cc b/ash/system/monitor/tray_monitor.cc
index b6f134a3c1084f9cfd15d4d81484aa362a834acd..e34ffb54a03dfd9711f17ea7cb0911930fc185e6 100644
--- a/ash/system/monitor/tray_monitor.cc
+++ b/ash/system/monitor/tray_monitor.cc
@@ -65,12 +65,12 @@ void TrayMonitor::OnGotHandles(const std::list<base::ProcessHandle>& handles) {
   std::string output;
   string16 free_bytes =
       ui::FormatBytes(static_cast<int64>(mem_info.free) * 1024);
-  output = StringPrintf("free: %s", UTF16ToUTF8(free_bytes).c_str());
+  output = base::StringPrintf("free: %s", UTF16ToUTF8(free_bytes).c_str());
   if (mem_info.gem_size != -1) {
     string16 gem_size = ui::FormatBytes(mem_info.gem_size);
-    output += StringPrintf("  gmem: %s", UTF16ToUTF8(gem_size).c_str());
+    output += base::StringPrintf("  gmem: %s", UTF16ToUTF8(gem_size).c_str());
     if (mem_info.gem_objects != -1)
-      output += StringPrintf("  gobjects: %d", mem_info.gem_objects);
+      output += base::StringPrintf("  gobjects: %d", mem_info.gem_objects);
   }
   size_t total_private_bytes = 0, total_shared_bytes = 0;
   for (std::list<base::ProcessHandle>::const_iterator i = handles.begin();
@@ -85,9 +85,9 @@ void TrayMonitor::OnGotHandles(const std::list<base::ProcessHandle>& handles) {
   string16 private_size = ui::FormatBytes(total_private_bytes);
   string16 shared_size = ui::FormatBytes(total_shared_bytes);
 
-  output += StringPrintf("\nGPU private: %s  shared: %s",
-                         UTF16ToUTF8(private_size).c_str(),
-                         UTF16ToUTF8(shared_size).c_str());
+  output += base::StringPrintf("\nGPU private: %s  shared: %s",
+                               UTF16ToUTF8(private_size).c_str(),
+                               UTF16ToUTF8(shared_size).c_str());
   label_->SetText(UTF8ToUTF16(output));
   refresh_timer_.Start(FROM_HERE,
       base::TimeDelta::FromMilliseconds(kRefreshTimeoutMs),