Transmit a X-Chrome-UMA-Enabled bit to Google domains from clients that have UMA enabled.

chrome/browser/profiles/profile_io_data.h

Index: chrome/browser/profiles/profile_io_data.h
diff --git a/chrome/browser/profiles/profile_io_data.h b/chrome/browser/profiles/profile_io_data.h
index 4adb1b11a2a6f0b61eb63bd37ae1c10a90dd1505..19fd31b74b3f6a80103e27abe8207999029d791d 100644
--- a/chrome/browser/profiles/profile_io_data.h
+++ b/chrome/browser/profiles/profile_io_data.h
@@ -183,6 +183,10 @@ class ProfileIOData {
     return &enable_referrers_;
   }
 
+  BooleanPrefMember* enable_metrics() const {
+    return &enable_metrics_;
+  }
+
   ChromeURLDataManagerBackend* chrome_url_data_manager_backend() const {
     return chrome_url_data_manager_backend_.get();
   }
@@ -272,6 +276,7 @@ class ProfileIOData {
 
   // Member variables which are pointed to by the various context objects.
   mutable BooleanPrefMember enable_referrers_;
+  mutable BooleanPrefMember enable_metrics_;
   mutable BooleanPrefMember clear_local_state_on_exit_;
   mutable BooleanPrefMember safe_browsing_enabled_;
   // TODO(marja): Remove session_startup_pref_ if no longer needed.