Add Desktop iOS promotion logging to chrome ios app.

ios/chrome/browser/desktop_promotion/desktop_promotion_sync_observer.mm

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "ios/chrome/browser/desktop_promotion/desktop_promotion_sync_observer.h"
+
+#include <memory>
+
+#include "base/metrics/histogram.h"
+#include "base/strings/stringprintf.h"
+#include "base/time/time.h"
+#include "components/browser_sync/profile_sync_service.h"
+#include "components/prefs/pref_service.h"
+#include "ios/chrome/browser/browser_state/chrome_browser_state.h"
+#include "ios/chrome/browser/desktop_promotion/desktop_promotion_prefs.h"
+#include "ios/chrome/browser/sync/ios_chrome_profile_sync_service_factory.h"
+
+namespace {
+
+const int kMaxEntrypoints = 5;

[pkl (ping after 24h if needed), 2017/01/18 23:47:02]

What is the maximum number of entry points?
I'm confused by this.

[mrefaat1, 2017/01/19 05:17:30]

Required by uma when logging count/enum .

+const char* kDesktopIOSPromotionEntrypointHistogramPrefix[] = {
+    "SavePasswordsNewBubble", "BookmarksNewBubble", "BookmarksExistingBubble",
+    "HistoryPage"};
+const char kSMSSentIOSSigninReasonHistogram[] =
+    "DesktopIOSPromotion.SMSSent.IOSSigninReason";
+const char kNoSMSIOSSigninReasonHistogram[] =
+    "DesktopIOSPromotion.NoSMS.IOSSigninReason";
+}
+
+DesktopPromotionSyncObserver::DesktopPromotionSyncObserver(
+    ios::ChromeBrowserState* browser_state)
+    : browser_state_(browser_state) {
+  browser_sync::ProfileSyncService* sync_service =
+      IOSChromeProfileSyncServiceFactory::GetForBrowserState(browser_state_);
+  sync_service->AddObserver(this);
+}
+
+DesktopPromotionSyncObserver::~DesktopPromotionSyncObserver() {
+  browser_sync::ProfileSyncService* sync_service =
+      IOSChromeProfileSyncServiceFactory::GetForBrowserState(browser_state_);
+  sync_service->RemoveObserver(this);
+}
+
+void DesktopPromotionSyncObserver::OnStateChanged() {
+  browser_sync::ProfileSyncService* sync_service =
+      IOSChromeProfileSyncServiceFactory::GetForBrowserState(browser_state_);
+  if (!desktop_metrics_logger_initiated_ &&
+      sync_service->GetActiveDataTypes().Has(syncer::PRIORITY_PREFERENCES)) {

[pkl (ping after 24h if needed), 2017/01/18 23:47:02]

If a user (cold) launches Chrome multiple times during the first 7 days,
wouldn't this cause the histograms to be logged multiple times?

[mrefaat1, 2017/01/19 05:17:30]

thanks for the case, i should check for the completion priority pref too.

+    desktop_metrics_logger_initiated_ = true;
+    PrefService* prefs = browser_state_->GetPrefs();
+    double last_interaction =
+        prefs->GetDouble(prefs::kDesktopIOSPromotionLastInteraction);
+    base::TimeDelta delta =
+        base::Time::Now() - base::Time::FromDoubleT(last_interaction);
+    if (delta.InDays() < 7) {
+      // This user have seen the promotion in the last 7 days so it may be a
+      // reason of the installation.
+      int sms_entrypoint =
+          prefs->GetInteger(prefs::kDesktopIOSPromotionSMSEntryPoint);
+      int targeted_entrypoints =
+          prefs->GetInteger(prefs::kDesktopIOSPromotionTargetedEntryPoints);
+      for (int i = 1; i < kMaxEntrypoints; i++) {

[pkl (ping after 24h if needed), 2017/01/18 23:47:02]

It would be helpful to have a comment explaining why this loop doesn't start
with i = 0.

[mrefaat1, 2017/01/19 05:17:30]

Acknowledged.

+        if (sms_entrypoint == i) {
+          UMA_HISTOGRAM_ENUMERATION(kSMSSentIOSSigninReasonHistogram, i,
+                                    kMaxEntrypoints);
+          UMA_HISTOGRAM_COUNTS(
+              base::StringPrintf(
+                  "DesktopIOSPromotion.%s.CompletionTime",

[pkl (ping after 24h if needed), 2017/01/18 23:47:02]

This probably doesn't work. See base/metrics/histogram_macros.h which states:
"...must be called with |name| as a runtime constant..."

[mrefaat1, 2017/01/19 05:17:30]

I think runtime constant (not compile time constant) here means that we
shouldn't change the string value after using it - because the uma logging macro
doesn't copy the string it uses the same reference that is given to it by the
call.
Based on that I think it's okay to pass the string output of StringPrintf -
which is std::string created inside the StringPrintf and doesn't change later.

+                  kDesktopIOSPromotionEntrypointHistogramPrefix[i - 1]),
+              delta.InHours());
+        } else {
+          if ((1 << i) & targeted_entrypoints)
+            UMA_HISTOGRAM_ENUMERATION(kNoSMSIOSSigninReasonHistogram, i,
+                                      kMaxEntrypoints);
+        }
+      }
+      prefs->SetBoolean(prefs::kDesktopIOSPromotionDone, true);
+    }
+  }
+}