Use base namespace for string16 in components and cloud_print.

cloud_print/virtual_driver/win/virtual_driver_helpers.cc

Index: cloud_print/virtual_driver/win/virtual_driver_helpers.cc
diff --git a/cloud_print/virtual_driver/win/virtual_driver_helpers.cc b/cloud_print/virtual_driver/win/virtual_driver_helpers.cc
index e214529507bdeb8310062cdf1f23c3396d7e0ecc..26a2bdfb7019fef7051ebd40c645615d06aa7aad 100644
--- a/cloud_print/virtual_driver/win/virtual_driver_helpers.cc
+++ b/cloud_print/virtual_driver/win/virtual_driver_helpers.cc
@@ -17,15 +17,16 @@ namespace cloud_print {
 
 const size_t kMaxMessageLen = 100;
 
-void DisplayWindowsMessage(HWND hwnd, HRESULT hr, const string16 &caption) {
+void DisplayWindowsMessage(HWND hwnd, HRESULT hr,
+                           const base::string16 &caption) {
   ::MessageBox(hwnd, GetErrorMessage(hr).c_str(), caption.c_str(), MB_OK);
 }
 
-string16 GetPortMonitorDllName() {
+base::string16 GetPortMonitorDllName() {
   if (IsSystem64Bit()) {
-    return string16(L"gcp_portmon64.dll");
+    return base::string16(L"gcp_portmon64.dll");
   } else {
-    return string16(L"gcp_portmon.dll");
+    return base::string16(L"gcp_portmon.dll");
   }
 }