Add UMA to determine how often we offline a page with previews.

chrome/browser/offline_pages/background_loader_offliner_unittest.cc

 // Copyright 2016 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.
 
 #include "chrome/browser/offline_pages/background_loader_offliner.h"
 
 #include "base/bind.h"
 #include "base/run_loop.h"
 #include "base/test/histogram_tester.h"
 #include "base/test/scoped_feature_list.h"
 #include "base/test/scoped_mock_time_message_loop_task_runner.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "chrome/browser/android/offline_pages/offliner_helper.h"
+#include "chrome/browser/loader/chrome_navigation_data.h"
 #include "chrome/browser/net/prediction_options.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/test/base/testing_profile.h"
 #include "components/content_settings/core/common/pref_names.h"
 #include "components/offline_pages/content/background_loader/background_loader_contents_stub.h"
 #include "components/offline_pages/core/background/load_termination_listener.h"
 #include "components/offline_pages/core/background/offliner.h"
 #include "components/offline_pages/core/background/offliner_policy.h"
 #include "components/offline_pages/core/background/save_page_request.h"
 #include "components/offline_pages/core/offline_page_feature.h"
@@ skipping 539 matching lines @@
   offliner()->DidFinishNavigation(handle.get());
   // NavigationHandle is always destroyed after finishing navigation.
   handle.reset();
   CompleteLoading();
   PumpLoop();
 
   EXPECT_TRUE(completion_callback_called());
   EXPECT_EQ(Offliner::RequestStatus::LOADING_FAILED_NO_NEXT, request_status());
 }
 
+TEST_F(BackgroundLoaderOfflinerTest, OffliningPreviewsStatusHistogram) {
+  base::Time creation_time = base::Time::Now();
+  SavePageRequest request(kRequestId, kHttpUrl, kClientId, creation_time,
+                          kUserRequested);
+  EXPECT_TRUE(offliner()->LoadAndSave(request, completion_callback(),
+                                      progress_callback()));
+
+  // Called after calling LoadAndSave so we have web_contents to work with.
+  std::unique_ptr<content::NavigationHandle> handle(
+      content::NavigationHandle::CreateNavigationHandleForTesting(
+          kHttpUrl, offliner()->web_contents()->GetMainFrame(), true,
+          net::Error::OK));
+  // Call DidFinishNavigation with handle.
+  offliner()->DidFinishNavigation(handle.get());
+
+  histograms().ExpectBucketCount(
+      "OfflinePages.Background.OffliningPreviewStatus.async_loading",
+      0,  // PreviewsOff

[RyanSturm, 2017/06/02 20:50:34]

Seems like you should have a test for PreviewsOn as well.

WebContentsTester exposes a method for setting the navigation data.

https://cs.chromium.org/chromium/src/content/public/test/web_contents_tester....

The implementation is fairly straightforward, so I believe you could just call
it with the web_contents_tester() and any navigationhandle.

[Pete Williamson, 2017/06/02 21:40:32]

I did try that, but it turns out to be problematic, because the call to
set_navigation_data() forced me to include a header file that is forbidden by
deps of the unit test.  Know any good workarounds?

[RyanSturm, 2017/06/02 22:14:25]

I think that header is already added to this unittest on line 31. Maybe you
tried to include content/browser/frame_host/navigation_handle_impl.h instead of
web_contents_tester.h

[Pete Williamson, 2017/06/02 23:17:41]

Yep, that worked, test added.  We now test both off and on.

+      1);
+}
+
 TEST_F(BackgroundLoaderOfflinerTest, OnlySavesOnceOnMultipleLoads) {
   base::Time creation_time = base::Time::Now();
   SavePageRequest request(kRequestId, kHttpUrl, kClientId, creation_time,
                           kUserRequested);
   EXPECT_TRUE(offliner()->LoadAndSave(request, completion_callback(),
                                       progress_callback()));
   // First load
   CompleteLoading();
   // Second load
   CompleteLoading();
@@ skipping 114 matching lines @@
   CompleteLoading();
   PumpLoop();
 
   // One extra part should be added if the flag is on.
   content::MHTMLExtraParts* extra_parts =
       content::MHTMLExtraParts::FromWebContents(offliner()->web_contents());
   EXPECT_EQ(extra_parts->size(), 1);
 }
 
 }  // namespace offline_pages