Introduce IOSChromeMetricsServicesManagerClient

ios/chrome/browser/chrome_switches.cc

Index: ios/chrome/browser/chrome_switches.cc
diff --git a/ios/chrome/browser/chrome_switches.cc b/ios/chrome/browser/chrome_switches.cc
index 705afcd9bad5f2da87b749504a001f6cfb7197a4..9105c70696842fc670654439ac63e5c17e0bb4e2 100644
--- a/ios/chrome/browser/chrome_switches.cc
+++ b/ios/chrome/browser/chrome_switches.cc
@@ -34,4 +34,11 @@ const char kEnableReaderModeToolbarIcon[] = "enable-reader-mode-toolbar-icon";
 // Disables support for keyboard commands.
 const char kDisableKeyboardCommands[] = "disable-keyboard-commands";
 
+// Enables the recording of metrics reports but disables reporting. In contrast
+// to kDisableMetrics, this executes all the code that a normal client would
+// use for reporting, except the report is dropped rather than sent to the
+// server. This is useful for finding issues in the metrics code during UI and
+// performance tests.
+const char kIOSMetricsRecordingOnly[] = "metrics-recording-only";
+
 }  // namespace switches