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

chrome/browser/offline_pages/background_loader_offliner.cc

Index: chrome/browser/offline_pages/background_loader_offliner.cc
diff --git a/chrome/browser/offline_pages/background_loader_offliner.cc b/chrome/browser/offline_pages/background_loader_offliner.cc
index 7860f5ead47813c7344b9f438ac634b6232ec01b..15dc7dda7c9fb3962c4e3c083a016d637ac95b69 100644
--- a/chrome/browser/offline_pages/background_loader_offliner.cc
+++ b/chrome/browser/offline_pages/background_loader_offliner.cc
@@ -12,6 +12,7 @@
 #include "base/time/time.h"
 #include "chrome/browser/android/offline_pages/offline_page_mhtml_archiver.h"
 #include "chrome/browser/android/offline_pages/offliner_helper.h"
+#include "chrome/browser/loader/chrome_navigation_data.h"
 #include "chrome/browser/profiles/profile.h"
 #include "components/offline_pages/core/background/offliner_policy.h"
 #include "components/offline_pages/core/background/save_page_request.h"
@@ -24,6 +25,7 @@
 #include "content/public/browser/render_frame_host.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_contents_user_data.h"
+#include "content/public/common/previews_state.h"
 
 namespace offline_pages {
 
@@ -73,6 +75,18 @@ void RecordErrorCauseUMA(const ClientId& client_id, net::Error error_code) {
       std::abs(error_code));
 }
 
+void RecordOffliningPreviewsUMA(const ClientId& client_id,
+                                content::PreviewsState previews_state) {
+  int is_previews_enabled = 0;
+  if (previews_state != content::PreviewsTypes::PREVIEWS_OFF)

[RyanSturm, 2017/06/05 20:43:59]

There is some subtlety with PREVIEWS_OFF vs PREVIEWS_NO_TRANSFORM. PREVIEWS_OFF
can actually have a server previews (like LoFi or LitePages), but this can only
happen when a user is opted into lite page previews via flags.

It's an area we are still sorting out. However,
ChromeNavigationData->data_reduction_proxy_data()->lite_page_received() will
tell if it is a lite page. I don't think there is a way to currently get LoFi
images without the bits set fortunately.

How about the condition checks
(ChromeNavigationData->data_reduction_proxy_data()->lite_page_received() ||
!(previews_state == content::PreviewsTypes::PREVIEWS_OFF || previews_state ==
content::PreviewsTypes::PREVIEWS_OFF))

Sorry about the confusion as this model is changing slightly throughout M61.
Perhaps dougarnett@ could take a look to make sure this set of checks will be
sufficient.

[Pete Williamson, 2017/06/05 21:40:47]

Added checks as you suggest (but worded slightly differently)

+    is_previews_enabled = 1;
+
+  UMA_HISTOGRAM_ENUMERATION(
+      AddHistogramSuffix(client_id,
+                         "OfflinePages.Background.OffliningPreviewStatus"),
+      is_previews_enabled, 2);
+}
+
 void HandleLoadTerminationCancel(
     const Offliner::CompletionCallback& completion_callback,
     const SavePageRequest& canceled_request) {
@@ -311,6 +325,21 @@ void BackgroundLoaderOffliner::DidFinishNavigation(
         page_load_state_ = RETRIABLE;
     }
   }
+
+  // Record UMA if we are offlining a previvew instead of an unmodified page.
+  // As documented in content/public/browser/navigation_handle.h, this
+  // NavigationData is a clone of the NavigationData instance returned from
+  // ResourceDispatcherHostDelegate::GetNavigationData during commit.
+  // Because ChromeResourceDispatcherHostDelegate always returns a
+  // ChromeNavigationData, it is safe to static_cast here.
+  ChromeNavigationData* navigation_data = static_cast<ChromeNavigationData*>(
+      navigation_handle->GetNavigationData());
+
+  content::PreviewsState previews_state = content::PreviewsTypes::PREVIEWS_OFF;
+  if (navigation_data)
+    previews_state = navigation_data->previews_state();
+
+  RecordOffliningPreviewsUMA(pending_request_->client_id(), previews_state);
 }
 
 void BackgroundLoaderOffliner::SetSnapshotControllerForTest(