Histogram the scheme of an origin on the 1st navigation to it.

chrome/browser/tab_contents/navigation_metrics_recorder.cc

Index: chrome/browser/tab_contents/navigation_metrics_recorder.cc
diff --git a/chrome/browser/tab_contents/navigation_metrics_recorder.cc b/chrome/browser/tab_contents/navigation_metrics_recorder.cc
index 8ee3fdd80a8aeb4aae3ec7fd496eb3e746a524c9..9775797160186b1a31bf512ebe88d3a4715cd251 100644
--- a/chrome/browser/tab_contents/navigation_metrics_recorder.cc
+++ b/chrome/browser/tab_contents/navigation_metrics_recorder.cc
@@ -7,14 +7,17 @@
 #include "base/metrics/histogram_macros.h"
 #include "build/build_config.h"
 #include "chrome/browser/browser_process.h"
+#include "chrome/browser/profiles/profile_io_data.h"
 #include "components/navigation_metrics/navigation_metrics.h"
 #include "components/rappor/rappor_utils.h"
+#include "content/public/browser/browser_context.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/navigation_details.h"
 #include "content/public/browser/navigation_entry.h"
 #include "content/public/browser/render_view_host.h"
 #include "content/public/browser/render_widget_host.h"
 #include "content/public/browser/render_widget_host_view.h"
+#include "content/public/browser/web_contents.h"
 #include "content/public/common/frame_navigate_params.h"
 #include "url/gurl.h"
 
@@ -36,8 +39,20 @@ void NavigationMetricsRecorder::DidNavigateMainFrame(
       const content::LoadCommittedDetails& details,
       const content::FrameNavigateParams& params) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
-  navigation_metrics::RecordMainFrameNavigation(details.entry->GetVirtualURL(),
-                                                details.is_in_page);
+  bool is_otr = web_contents()->GetBrowserContext()->IsOffTheRecord();

[felt, 2016/04/01 00:01:59]

IsOffTheRecord only returns true for Incognito, right? the comment at its
definition says so, but I remember pkasting suggesting otherwise (something to
do with guest mode?).

[palmer, 2016/04/05 23:42:18]

OTR is for Incognito and Guest Mode. Rather than try to replicate the internals
of BrowserContext::IsOffTheRecord, I'll just record
Navigation.SchemePerUniqueOrigin and Navigation.SchemePerUniqueOriginOTR, and
use the "OTR" nomenclature consistently in this CL. Sound good?

+  bool should_record_main_frame_navigation = true;
+  if (is_otr) {
+    content::ResourceContext* context =
+        web_contents()->GetBrowserContext()->GetResourceContext();
+    ProfileIOData* io_data = ProfileIOData::FromResourceContext(context);
+    url::Origin origin(details.entry->GetVirtualURL());
+    if (io_data->HaveAlreadySeenOrigin(origin))
+      should_record_main_frame_navigation = false;
+  }
+  if (should_record_main_frame_navigation) {
+    navigation_metrics::RecordMainFrameNavigation(
+        details.entry->GetVirtualURL(), details.is_in_page, is_otr);
+  }
   // Record the domain and registry of the URL that resulted in a navigation to
   // a |data:| URL, either by redirects or user clicking a link.
   if (details.entry->GetVirtualURL().SchemeIs(url::kDataScheme) &&