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_macros.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/desktop_promotion/desktop_promotion_prefs.h"
+#include "ios/chrome/browser/desktop_promotion/histogram_macros.h"
+
+namespace {
+
+const char* kDesktopIOSPromotionEntrypointHistogramPrefix[] = {
+    "SavePasswordsNewBubble", "BookmarksNewBubble", "BookmarksExistingBubble",
+    "HistoryPage"};

[sdefresne, 2017/01/26 17:03:25]

Can you put a comma after "HistoryPage" so that clang-format do not format this
code weirdly?

[mrefaat, 2017/01/26 23:34:12]

Done.

+}
+
+DesktopPromotionSyncObserver::DesktopPromotionSyncObserver(
+    PrefService* pref_service,
+    browser_sync::ProfileSyncService* sync_service)
+    : pref_service_(pref_service), sync_service_(sync_service) {
+  DCHECK(pref_service_);
+  DCHECK(sync_service_);
+  sync_service_->AddObserver(this);
+}
+
+DesktopPromotionSyncObserver::~DesktopPromotionSyncObserver() {
+  sync_service_->RemoveObserver(this);
+}
+
+void DesktopPromotionSyncObserver::OnStateChanged() {
+  if (desktop_metrics_logger_initiated_ ||
+      !sync_service_->GetActiveDataTypes().Has(syncer::PRIORITY_PREFERENCES)) {
+    return;
+  }
+
+  desktop_metrics_logger_initiated_ = true;
+  bool done_logging =
+      pref_service_->GetBoolean(prefs::kDesktopIOSPromotionDone);
+  double last_impression =
+      pref_service_->GetDouble(prefs::kDesktopIOSPromotionLastImpression);
+  base::TimeDelta delta =
+      base::Time::Now() - base::Time::FromDoubleT(last_impression);
+  if (done_logging || delta.InDays() >= 7) {
+    return;
+  }
+
+  // This user have seen the promotion in the last 7 days so it may be a
+  // reason of the installation.
+  int sms_entrypoint =
+      pref_service_->GetInteger(prefs::kDesktopIOSPromotionSMSEntryPoint);
+  int targeted_entrypoints =
+      pref_service_->GetInteger(prefs::kDesktopIOSPromotionTargetedEntryPoints);
+
+  // Entry points are represented on the preference by integers [1..4].

[Mark P, 2017/01/26 18:55:15]

Where is the meaning of these entry points defined?  It needs the standard
warning.
https://chromium.googlesource.com/chromium/src.git/+/HEAD/tools/metrics/histo...

[mrefaat, 2017/01/26 23:34:12]

The meaning will be set on the desktop side code, and will add the warning
there. i've put a todo for now

+  int entrypoint_prefixes_count =
+      arraysize(kDesktopIOSPromotionEntrypointHistogramPrefix);
+  for (int i = 1; i < entrypoint_prefixes_count + 1; i++) {
+    if (sms_entrypoint == i) {
+      UMA_HISTOGRAM_ENUMERATION("DesktopIOSPromotion.SMSSent.IOSSigninReason",
+                                i, entrypoint_prefixes_count + 1);
+      UMA_HISTOGRAM_COUNT_1000_NO_CACHE(

[Mark P, 2017/01/26 18:55:15]

Please don't use histogram macros from chromecast/

Use FactoryGet yourself; that's typically how chromium developers do it.

[mrefaat, 2017/01/26 23:34:12]

These are not chromecast macros' - i defined another file
ios/chrome/browser/desktop_promotion/histogram_macros.h where i use the
FactoryGet

+          base::StringPrintf(
+              "DesktopIOSPromotion.%s.CompletionTime",
+              kDesktopIOSPromotionEntrypointHistogramPrefix[i - 1]),
+          delta.InHours());

[Mark P, 2017/01/26 18:55:15]

Consider explicitly emitting something (0?) if this time is negative, which is
possible given how it's calculated.

[mrefaat, 2017/01/26 23:34:12]

Acknowledged.

+    } else {
+      // If the user saw this promotion type, log that it could be a reason
+      // for the signin.
+      if ((1 << i) & targeted_entrypoints)
+        UMA_HISTOGRAM_ENUMERATION("DesktopIOSPromotion.NoSMS.IOSSigninReason",
+                                  i, entrypoint_prefixes_count + 1);
+    }
+  }
+  pref_service_->SetBoolean(prefs::kDesktopIOSPromotionDone, true);
+}