BackForwardCache: Add tests for CLS scores

Bug: 1014174
Change-Id: Ia75170ea791b5c8ffff100f58af1a7f65497b882
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2283037
Commit-Queue: Hajime Hoshi <hajimehoshi@chromium.org>
Reviewed-by: Nicolás Peña Moreno <npm@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#790789}

chrome/browser/page_load_metrics/observers/back_forward_cache_page_load_metrics_observer_browsertest.cc

@@ -188,12 +188,23 @@ IN_PROC_BROWSER_TEST_F(BackForwardCachePageLoadMetricsObserverBrowserTest,
 
 IN_PROC_BROWSER_TEST_F(BackForwardCachePageLoadMetricsObserverBrowserTest,
                        CumulativeLayoutShiftAfterBackForwardCacheRestore) {
-  ASSERT_TRUE(embedded_test_server()->Start());
-  GURL url_a(embedded_test_server()->GetURL("a.com", "/title1.html"));
+  Start();
+
+  const char path[] = "/layout-instability/simple-block-movement.html";
+  GURL url_a(embedded_test_server()->GetURL("a.com", path));
   GURL url_b(embedded_test_server()->GetURL("b.com", "/title1.html"));
 
   // Navigate to A.
-  EXPECT_TRUE(ui_test_utils::NavigateToURL(browser(), url_a));
+  {
+    auto waiter = CreatePageLoadMetricsTestWaiter();
+    waiter->AddPageExpectation(
+        page_load_metrics::PageLoadMetricsTestWaiter::TimingField::kFirstPaint);
+    waiter->AddPageExpectation(page_load_metrics::PageLoadMetricsTestWaiter::
+                                   TimingField::kLayoutShift);
+    EXPECT_TRUE(ui_test_utils::NavigateToURL(browser(), url_a));
+    waiter->Wait();
+  }
+
   content::RenderFrameHost* rfh_a = top_frame_host();
 
   // Navigate to B.
@@ -201,10 +212,35 @@ IN_PROC_BROWSER_TEST_F(BackForwardCachePageLoadMetricsObserverBrowserTest,
   EXPECT_TRUE(rfh_a->IsInBackForwardCache());
 
   // Go back to A.
-  web_contents()->GetController().GoBack();
-  EXPECT_TRUE(WaitForLoadStop(web_contents()));
-  EXPECT_EQ(rfh_a, top_frame_host());
-  EXPECT_FALSE(rfh_a->IsInBackForwardCache());
+  double next_score;
+  {
+    auto waiter = CreatePageLoadMetricsTestWaiter();
+    waiter->AddPageExpectation(
+        page_load_metrics::PageLoadMetricsTestWaiter::TimingField::
+            kFirstPaintAfterBackForwardCacheRestore);
+    waiter->AddPageExpectation(page_load_metrics::PageLoadMetricsTestWaiter::
+                                   TimingField::kLayoutShift);
+    web_contents()->GetController().GoBack();
+    EXPECT_TRUE(WaitForLoadStop(web_contents()));
+    EXPECT_EQ(rfh_a, top_frame_host());
+    EXPECT_FALSE(rfh_a->IsInBackForwardCache());
+
+    base::ListValue expectations =
+        EvalJs(web_contents(), "cls_run_tests").ExtractList();
+    next_score = EvalJs(web_contents(),
+                        R"((async() => {
+const shifter = document.querySelector('#shifter');
+const currentTop =
+  parseInt(getComputedStyle(shifter).getPropertyValue('top'), 10);
+const newTop = 320;
+shifter.style.top = newTop + 'px';
+const score = computeExpectedScore(
+    300 * (200 + newTop - currentTop), newTop - currentTop);
+return score;
+})())")
+                     .ExtractDouble();
+    waiter->Wait();
+  }
 
   // The RenderFrameHost for the page B was likely in the back-forward cache
   // just after the history navigation, but now this might be evicted due to
@@ -216,7 +252,13 @@ IN_PROC_BROWSER_TEST_F(BackForwardCachePageLoadMetricsObserverBrowserTest,
   EXPECT_TRUE(ui_test_utils::NavigateToURL(browser(), url_b));
   EXPECT_TRUE(rfh_a->IsInBackForwardCache());
 
-  // As A enters to the back-forward cache once, CLS is recorded.
+  auto samples = histogram_tester().GetAllSamples(
+      internal::
+          kHistogramCumulativeShiftScoreMainFrameAfterBackForwardCacheRestore);
+  EXPECT_EQ(1ul, samples.size());
+  EXPECT_EQ(base::Bucket(page_load_metrics::LayoutShiftUmaValue(next_score), 1),
+            samples[0]);
+
   histogram_tester().ExpectTotalCount(
       internal::
           kHistogramCumulativeShiftScoreMainFrameAfterBackForwardCacheRestore,

components/page_load_metrics/browser/page_load_metrics_test_waiter.cc

@@ -105,7 +105,15 @@ void PageLoadMetricsTestWaiter::OnTimingUpdated(
   const page_load_metrics::mojom::FrameMetadata& metadata =
       subframe_rfh ? GetDelegateForCommittedLoad().GetSubframeMetadata()
                    : GetDelegateForCommittedLoad().GetMainFrameMetadata();
-  TimingFieldBitSet matched_bits = GetMatchedBits(timing, metadata);
+  // There is no way to get the layout shift score only for a subframe so far.
+  // See the score only when the frame is the main frame.
+  const PageRenderData* render_data =
+      subframe_rfh ? nullptr
+                   : &GetDelegateForCommittedLoad().GetMainFrameRenderData();
+
+  TimingFieldBitSet matched_bits =
+      GetMatchedBits(timing, metadata, render_data);
+
   if (subframe_rfh) {
     subframe_expected_fields_.ClearMatching(matched_bits);
   } else {
@@ -224,7 +232,8 @@ void PageLoadMetricsTestWaiter::FrameSizeChanged(
 PageLoadMetricsTestWaiter::TimingFieldBitSet
 PageLoadMetricsTestWaiter::GetMatchedBits(
     const page_load_metrics::mojom::PageLoadTiming& timing,
-    const page_load_metrics::mojom::FrameMetadata& metadata) {
+    const page_load_metrics::mojom::FrameMetadata& metadata,
+    const PageRenderData* render_data) {
   PageLoadMetricsTestWaiter::TimingFieldBitSet matched_bits;
   if (timing.document_timing->load_event_start)
     matched_bits.Set(TimingField::kLoadEvent);
@@ -258,6 +267,13 @@ PageLoadMetricsTestWaiter::GetMatchedBits(
     }
   }
 
+  if (render_data) {
+    double layout_shift_score = render_data->layout_shift_score;
+    if (last_main_frame_layout_shift_score_ < layout_shift_score)
+      matched_bits.Set(TimingField::kLayoutShift);
+    last_main_frame_layout_shift_score_ = layout_shift_score;
+  }
+
   return matched_bits;
 }
 

components/page_load_metrics/browser/page_load_metrics_test_waiter.h

@@ -33,6 +33,7 @@ class PageLoadMetricsTestWaiter
     kFirstInputDelay = 1 << 8,
     kFirstPaintAfterBackForwardCacheRestore = 1 << 9,
     kFirstInputDelayAfterBackForwardCacheRestore = 1 << 10,
+    kLayoutShift = 1 << 11,
   };
   using FrameTreeNodeId =
       page_load_metrics::PageLoadMetricsObserver::FrameTreeNodeId;
@@ -181,9 +182,10 @@ class PageLoadMetricsTestWaiter
     bool operator()(const gfx::Size a, const gfx::Size b) const;
   };
 
-  static TimingFieldBitSet GetMatchedBits(
+  TimingFieldBitSet GetMatchedBits(
       const page_load_metrics::mojom::PageLoadTiming& timing,
-      const page_load_metrics::mojom::FrameMetadata& metadata);
+      const page_load_metrics::mojom::FrameMetadata& metadata,
+      const PageRenderData* render_data);
 
   // Updates observed page fields when a timing update is received by the
   // MetricsWebContentsObserver. Stops waiting if expectations are satsfied
@@ -280,6 +282,8 @@ class PageLoadMetricsTestWaiter
   bool attach_on_tracker_creation_ = false;
   bool did_add_observer_ = false;
 
+  double last_main_frame_layout_shift_score_ = 0;
+
   base::WeakPtrFactory<PageLoadMetricsTestWaiter> weak_factory_{this};
 };