Reland "Stop over-recording data use related to Previews"

This is a reland of 21fe97f0

Original change's description:
> Stop over-recording data use related to Previews
> 
> Lite Page Server Previews over records data use when it attempts to
> record data savings. Instead, only the savings should be recorded.
> 
> This also changes the data usage site breakdown code to use Virtual URL
> (the one in the omnibox) instead of the actual host for the sake of
> improving UI and tracking HTTPS Lite Page Previews more accurately.
> 
> Bug: 936577
> Change-Id: Ib7dfe8afeea0b277ac065d58c02b2962a4ab6c94
> Reviewed-on: https://chromium-review.googlesource.com/c/1492428
> Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
> Reviewed-by: Robert Ogden <robertogden@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#636282}

Bug: 936577
Change-Id: I342de5853cea0ffced06af1ac531846cdd1cc34b
Reviewed-on: https://chromium-review.googlesource.com/c/1494797Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636545}

chrome/browser/page_load_metrics/observers/data_saver_site_breakdown_metrics_observer.cc

@@ -37,7 +37,11 @@ DataSaverSiteBreakdownMetricsObserver::OnCommit(
   // will be called is in MetricsWebContentsObserver's destructor, which is
   // called in WebContents destructor.
   browser_context_ = navigation_handle->GetWebContents()->GetBrowserContext();
-  committed_host_ = navigation_handle->GetURL().HostNoBrackets();
+
+  // Use Virtual URL instead of actual host.
+  committed_host_ = navigation_handle->GetWebContents()
+                        ->GetLastCommittedURL()
+                        .HostNoBrackets();
   return CONTINUE_OBSERVING;
 }
 

chrome/browser/previews/previews_lite_page_browsertest.cc

@@ -1307,12 +1307,13 @@ IN_PROC_BROWSER_TEST_P(PreviewsLitePageServerBrowserTest,
   ui_test_utils::NavigateToURL(browser(), HttpsLitePageURL(kSuccess));
   VerifyPreviewLoaded();
 
+  base::RunLoop().RunUntilIdle();
+
   // Navigate to an untracked (no preview) page before checking reported savings
   // to reduce flakiness.
-  ui_test_utils::NavigateToURL(browser(), GURL("http://www.google.com"));
+  ui_test_utils::NavigateToURL(browser(), GURL(url::kAboutBlankURL));
 
   EXPECT_EQ(GetTotalOriginalContentLength() - GetTotalDataUsage(), 40U);
-  EXPECT_EQ(GetDataUsage(), 20U);
 }
 
 IN_PROC_BROWSER_TEST_P(PreviewsLitePageServerBrowserTest,

chrome/browser/previews/previews_lite_page_decider.cc

@@ -340,11 +340,14 @@ void PreviewsLitePageDecider::ReportDataSavings(int64_t network_bytes,
   if (!drp_settings_ || !drp_settings_->data_reduction_proxy_service())
     return;
 
+  // The total data usage is tracked for all data in Chrome, so we only need to
+  // update the savings.
+  int64_t data_saved = original_bytes - network_bytes;
   drp_settings_->data_reduction_proxy_service()->UpdateDataUseForHost(
-      network_bytes, original_bytes, host);
+      0, data_saved, host);
 
   drp_settings_->data_reduction_proxy_service()->UpdateContentLengths(
-      network_bytes, original_bytes, true /* data_reduction_proxy_enabled */,
+      0, data_saved, true /* data_reduction_proxy_enabled */,
       data_reduction_proxy::DataReductionProxyRequestType::
           VIA_DATA_REDUCTION_PROXY,
       "text/html", true /* is_user_traffic */,

chrome/browser/previews/previews_lite_page_navigation_throttle_manager.h

@@ -38,7 +38,8 @@ class PreviewsLitePageNavigationThrottleManager {
   // Generates a new page id for a request to the previews server.
   virtual uint64_t GeneratePageID() = 0;
 
-  // Reports data savings to Data Saver.
+  // Reports data savings to Data Saver. Only the difference in |original_bytes|
+  // and |network_bytes| will be updated in the data saver calls.
   virtual void ReportDataSavings(int64_t network_bytes,
                                  int64_t original_bytes,
                                  const std::string& host) = 0;