[Previews] Add offline check before HintsFetch.

Only attempt to fetch hints if the network is available.

Note: The Optimization Guide does not support iOS but is in components
due to supporting Previews. A future refactor of Previews may allow for
 moving Optimization Guide to the browser layer. An assertion was added
to the BUILD.gn file to make the iOS decision more clear.

Bug: 986817
Change-Id: Iafa4101b42147530e0b38f2d6a4eb36a7ddac37c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1715505Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Robert Ogden <robertogden@chromium.org>
Commit-Queue: Michael Crouse <mcrouse@chromium.org>
Cr-Commit-Position: refs/heads/master@{#681180}

chrome/browser/previews/hints_fetcher_browsertest.cc

@@ -40,6 +40,7 @@
 #include "components/previews/core/previews_switches.h"
 #include "content/public/browser/browser_task_traits.h"
 #include "content/public/test/browser_test_utils.h"
+#include "content/public/test/network_connection_change_simulator.h"
 #include "net/test/embedded_test_server/http_request.h"
 #include "net/test/embedded_test_server/http_response.h"
 #include "services/network/public/cpp/network_quality_tracker.h"
@@ -168,6 +169,11 @@ class HintsFetcherDisabledBrowserTest : public InProcessBrowserTest {
     run_loop.Run();
   }
 
+  void SetNetworkConnectionOffline() {
+    content::NetworkConnectionChangeSimulator().SetConnectionType(
+        network::mojom::ConnectionType::CONNECTION_NONE);
+  }
+
   // Seeds the Site Engagement Service with two HTTP and two HTTPS sites for the
   // current profile.
   void SeedSiteEngagementService() {
@@ -652,3 +658,30 @@ IN_PROC_BROWSER_TEST_F(
           optimization_guide::HintCacheStore::StoreEntryType::kComponentHint),
       0);
 }
+
+IN_PROC_BROWSER_TEST_F(
+    HintsFetcherBrowserTest,
+    DISABLE_ON_WIN_MAC_CHROMESOS(HintsFetcherNetworkOffline)) {
+  const base::HistogramTester* histogram_tester = GetHistogramTester();
+  GURL url = https_url();
+  base::CommandLine::ForCurrentProcess()->RemoveSwitch(
+      optimization_guide::switches::kFetchHintsOverride);
+  base::CommandLine::ForCurrentProcess()->AppendSwitch(
+      optimization_guide::switches::kFetchHintsOverrideTimer);
+
+  // Set the network to be offline.
+  SetNetworkConnectionOffline();
+
+  // Set the blacklist state to initialized so the sites in the engagement
+  // service will be used and not blacklisted on the first GetTopHosts
+  // request.
+  SetTopHostBlacklistState(optimization_guide::prefs::
+                               HintsFetcherTopHostBlacklistState::kInitialized);
+
+  // Whitelist NoScript for https_url()'s' host.
+  SetUpComponentUpdateHints(https_url());
+
+  // No HintsFetch should occur because the connection is offline.
+  histogram_tester->ExpectTotalCount(
+      "OptimizationGuide.HintsFetcher.GetHintsRequest.HostCount", 0);
+}

components/optimization_guide/BUILD.gn

@@ -2,6 +2,8 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+assert(!is_ios, "Optimization Guide is not available on iOS.")
+
 static_library("optimization_guide") {
   sources = [
     "bloom_filter.cc",
@@ -42,6 +44,7 @@ static_library("optimization_guide") {
     "//components/leveldb_proto",
     "//components/optimization_guide/proto:optimization_guide_proto",
     "//components/prefs",
+    "//content/public/browser",
     "//google_apis",
     "//net:net",
     "//services/network/public/cpp",

components/optimization_guide/DEPS

 include_rules = [
   "+components/leveldb_proto",
   "+components/prefs",
+  "+content/public/browser",
   "+google_apis",
   "+net",
   "+services/network",

components/optimization_guide/hints_fetcher.cc

@@ -12,12 +12,12 @@
 #include "base/metrics/histogram_macros.h"
 #include "components/optimization_guide/optimization_guide_features.h"
 #include "components/optimization_guide/proto/hints.pb.h"
+#include "content/public/browser/network_service_instance.h"
 #include "net/base/load_flags.h"
 #include "net/base/url_util.h"
 #include "net/http/http_request_headers.h"
 #include "net/http/http_response_headers.h"
 #include "net/http/http_status_code.h"
-#include "net/traffic_annotation/network_traffic_annotation.h"
 #include "services/network/public/cpp/shared_url_loader_factory.h"
 #include "services/network/public/cpp/simple_url_loader.h"
 
@@ -42,6 +42,11 @@ bool HintsFetcher::FetchOptimizationGuideServiceHints(
     HintsFetchedCallback hints_fetched_callback) {
   SEQUENCE_CHECKER(sequence_checker_);
 
+  if (content::GetNetworkConnectionTracker()->IsOffline()) {
+    std::move(hints_fetched_callback_).Run(base::nullopt);
+    return false;
+  }
+
   if (url_loader_)
     return false;