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

chrome/browser/renderer_host/chrome_resource_dispatcher_host_delegate.cc

Index: chrome/browser/renderer_host/chrome_resource_dispatcher_host_delegate.cc
diff --git a/chrome/browser/renderer_host/chrome_resource_dispatcher_host_delegate.cc b/chrome/browser/renderer_host/chrome_resource_dispatcher_host_delegate.cc
index f54de5dbcdf2d980ebc79b460e5a4cd4bf0de7dc..9e577f44d6b8c44c3c1ae81d472545fd6c71b471 100644
--- a/chrome/browser/renderer_host/chrome_resource_dispatcher_host_delegate.cc
+++ b/chrome/browser/renderer_host/chrome_resource_dispatcher_host_delegate.cc
@@ -12,6 +12,7 @@
 #include "chrome/browser/download/download_util.h"
 #include "chrome/browser/extensions/user_script_listener.h"
 #include "chrome/browser/external_protocol/external_protocol_handler.h"
+#include "chrome/browser/google/google_util.h"
 #include "chrome/browser/instant/instant_loader.h"
 #include "chrome/browser/net/load_timing_observer.h"
 #include "chrome/browser/prerender/prerender_manager.h"
@@ -163,6 +164,8 @@ void ChromeResourceDispatcherHostDelegate::RequestBeginning(
 #endif
   }
 
+  AppendChromeMetricsHeaders(request, resource_context, resource_type);
+
   AppendStandardResourceThrottles(request,
                                   resource_context,
                                   child_id,
@@ -293,6 +296,28 @@ void ChromeResourceDispatcherHostDelegate::AppendStandardResourceThrottles(
     throttles->push_back(throttle);
 }
 
+void ChromeResourceDispatcherHostDelegate::AppendChromeMetricsHeaders(
+    net::URLRequest* request,
+    content::ResourceContext* resource_context,
+    ResourceType::Type resource_type) {
+  // Note our criteria for attaching Chrome experiment headers:
+  // 1. We only transmit to *.google.<TLD> domains. NOTE that this use of
+  //    google_util helpers to check this does not guarantee that the URL is
+  //    Google-owned, only that it is of the form *.google.<TLD>. In the future
+  //    we may choose to reinforce this check.
+  // 2. We only transmit for non-Incognito profiles.
+  // 3. For the X-Chrome-UMA-Enabled bit, we only set it if UMA is in fact
+  //    enabled for this install of Chrome.
+  ProfileIOData* io_data = ProfileIOData::FromResourceContext(resource_context);
+  if (google_util::IsGoogleDomainUrl(request->url().spec(),
+                                     google_util::ALLOW_SUBDOMAIN) &&
+      !io_data->is_incognito() && io_data->enable_metrics()->GetValue()) {
+    request->SetExtraRequestHeaderByName("X-Chrome-UMA-Enabled",
+                                         "1",
+                                         false);
+  }
+}
+
 bool ChromeResourceDispatcherHostDelegate::ShouldForceDownloadResource(
     const GURL& url, const std::string& mime_type) {
   // Special-case user scripts to get downloaded instead of viewed.