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

chrome/browser/profiles/profile_io_data.cc

Index: chrome/browser/profiles/profile_io_data.cc
diff --git a/chrome/browser/profiles/profile_io_data.cc b/chrome/browser/profiles/profile_io_data.cc
index 3d439fb2d92992a0de46bce4b720a20f66bb01a6..606e84c6da5097ae6dfac23e7ca56cbac7092fcb 100644
--- a/chrome/browser/profiles/profile_io_data.cc
+++ b/chrome/browser/profiles/profile_io_data.cc
@@ -864,6 +864,10 @@ bool ProfileIOData::IsOffTheRecord() const {
       || profile_type() == Profile::GUEST_PROFILE;
 }
 
+bool ProfileIOData::HaveAlreadySeenOrigin(const url::Origin& origin) {
+  return origins_seen_.insert(origin).second == false;

[felt, 2016/04/07 02:28:04]

seems unexpected to me (based on method name & description) that this would also
insert the origin in addition to returning true/false

[palmer, 2016/04/07 23:45:43]

What would you rather do?

I want to let the caller not care about the details of keeping track of how we
remember origins we've seen and not seen, and I want to let the caller not have
to adhere to a multi-call protocol such as (hypothetical):

  if (!io_data->HaveAlreadySeen(origin)) {
    // Record UMA...
    io_data->NoteOriginSeen(origin);
  }

[felt, 2016/04/07 23:51:15]

I agree it makes sense to keep it a single method. I was suggesting naming it
something like CalculateRepeatVisit, InsertAndLookupOrigin, or adjusting the
comment to mention it isn't side effect free.

+}
+
 void ProfileIOData::InitializeMetricsEnabledStateOnUIThread() {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 #if BUILDFLAG(ANDROID_JAVA_UI)