[page_load_metrics] Add a NavigationThrottle for richer abort metrics

components/page_load_metrics/browser/metrics_web_contents_observer_unittest.cc

Index: components/page_load_metrics/browser/metrics_web_contents_observer_unittest.cc
diff --git a/components/page_load_metrics/browser/metrics_web_contents_observer_unittest.cc b/components/page_load_metrics/browser/metrics_web_contents_observer_unittest.cc
index 3c773cb94cf08942ded81dd8f04a8567d1b827a9..8e92777e9b25362b3a1d94dbf074a0b1e367fc18 100644
--- a/components/page_load_metrics/browser/metrics_web_contents_observer_unittest.cc
+++ b/components/page_load_metrics/browser/metrics_web_contents_observer_unittest.cc
@@ -12,6 +12,7 @@
 #include "base/process/kill.h"
 #include "base/test/histogram_tester.h"
 #include "base/time/time.h"
+#include "components/page_load_metrics/browser/metrics_navigation_throttle.h"
 #include "components/page_load_metrics/browser/page_load_metrics_observer.h"
 #include "components/page_load_metrics/common/page_load_metrics_messages.h"
 #include "content/public/browser/navigation_handle.h"
@@ -103,6 +104,20 @@ class TestPageLoadMetricsEmbedderInterface
 
 }  //  namespace
 
+class AddThrottleWebContentsObserver : public content::WebContentsObserver {
+ public:
+  AddThrottleWebContentsObserver(content::WebContents* contents)
+      : content::WebContentsObserver(contents) {}
+
+  void DidStartNavigation(content::NavigationHandle* handle) override {
+    handle->RegisterThrottleForTesting(
+        MetricsNavigationThrottle::Create(handle));
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(AddThrottleWebContentsObserver);
+};
+
 class MetricsWebContentsObserverTest
     : public content::RenderViewHostTestHarness {
  public:
@@ -127,9 +142,11 @@ class MetricsWebContentsObserverTest
 
   void AttachObserver() {
     embedder_interface_ = new TestPageLoadMetricsEmbedderInterface();
-    observer_.reset(new MetricsWebContentsObserver(
+    observer_.reset(MetricsWebContentsObserver::CreateForWebContents(
         web_contents(), base::WrapUnique(embedder_interface_)));
     observer_->WasShown();
+    add_throttling_observer_.reset(
+        new AddThrottleWebContentsObserver(web_contents()));
   }
 
   void CheckErrorEvent(InternalErrorLoadEvent error, int count) {
@@ -169,6 +186,7 @@ class MetricsWebContentsObserverTest
   base::HistogramTester histogram_tester_;
   TestPageLoadMetricsEmbedderInterface* embedder_interface_;
   std::unique_ptr<MetricsWebContentsObserver> observer_;
+  std::unique_ptr<AddThrottleWebContentsObserver> add_throttling_observer_;
 
  private:
   int num_errors_;
@@ -362,8 +380,12 @@ TEST_F(MetricsWebContentsObserverTest, BadIPC) {
 }
 
 TEST_F(MetricsWebContentsObserverTest, ObservePartialNavigation) {
-  // Delete the observer for this test, add it once the navigation has started.
-  observer_.reset();
+  // Reset the state of the tests, and attach the MetricsWebContentsObserver in
+  // the middle of a navigation. This tests that the class is robust to only
+  // observing some of a navigation.
+  DeleteContents();
+  SetContents(CreateTestWebContents());
+
   PageLoadTiming timing;
   timing.navigation_start = base::Time::FromDoubleT(10);