Remove duplicate implementations of string conversion methods.

webrtc/test/testsupport/iosfileutils.mm

Index: webrtc/test/testsupport/iosfileutils.mm
diff --git a/webrtc/test/testsupport/iosfileutils.mm b/webrtc/test/testsupport/iosfileutils.mm
index 6bbe0823853fd39a926b85aa290e3569158c3f54..04ffd0fb574f9f85950049e28d139fedf1d652d7 100644
--- a/webrtc/test/testsupport/iosfileutils.mm
+++ b/webrtc/test/testsupport/iosfileutils.mm
@@ -19,25 +19,13 @@
 
 #include "webrtc/base/checks.h"
 #include "webrtc/typedefs.h"
+#include "webrtc/sdk/objc/Framework/Classes/helpers.h"
 
 namespace webrtc {
 namespace test {
 
-// TODO(henrika): move to shared location.
-// See https://code.google.com/p/webrtc/issues/detail?id=4773 for details.
-NSString* NSStringFromStdString(const std::string& stdString) {
-  // std::string may contain null termination character so we construct
-  // using length.
-  return [[NSString alloc] initWithBytes:stdString.data()
-                                  length:stdString.length()
-                                encoding:NSUTF8StringEncoding];
-}
-
-std::string StdStringFromNSString(NSString* nsString) {
-  NSData* charData = [nsString dataUsingEncoding:NSUTF8StringEncoding];
-  return std::string(reinterpret_cast<const char*>([charData bytes]),
-                     [charData length]);
-}
+using webrtc::ios::NSStringFromStdString;
+using webrtc::ios::StdStringFromNSString;
 
 // For iOS, resource files are added to the application bundle in the root
 // and not in separate folders as is the case for other platforms. This method