Fix modules_unittests on iOS.

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 87b7397c7911d981c42a62a90f214f935d8a6838..6bbe0823853fd39a926b85aa290e3569158c3f54 100644
--- a/webrtc/test/testsupport/iosfileutils.mm
+++ b/webrtc/test/testsupport/iosfileutils.mm
@@ -54,6 +54,13 @@ std::string IOSResourcePath(std::string name, std::string extension) {
   }
 }
 
+std::string IOSRootPath() {
+  @autoreleasepool {
+    NSBundle* mainBundle = [NSBundle mainBundle];
+    return StdStringFromNSString(mainBundle.bundlePath) + "/";
+  }
+}
+
 // For iOS, we don't have access to the output directory. Return the path to the
 // temporary directory instead. This is mostly used by tests that need to write
 // output files to disk.