Send an event to the page load metrics to track resource starting.

chrome/browser/page_load_metrics/observers/resource_tracking_page_load_metrics_observer_unittest.cc

+// Copyright 2017 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/page_load_metrics/observers/resource_tracking_page_load_metrics_observer.h"
+
+#include "chrome/browser/page_load_metrics/observers/page_load_metrics_observer_test_harness.h"
+
+namespace {
+const char kFakeUrl[] = "http://www.google.com/nothingotseehere.html";
+}  // namespace
+
+namespace page_load_metrics {
+
+class ResourceTrackingPageLoadMetricsObserverTest
+    : public page_load_metrics::PageLoadMetricsObserverTestHarness {
+ public:
+  ResourceTrackingPageLoadMetricsObserverTest() : observer_(nullptr) {}
+
+ protected:
+  void RegisterObservers(page_load_metrics::PageLoadTracker* tracker) override {
+    std::unique_ptr<page_load_metrics::ResourceTrackingPageLoadMetricsObserver>
+        observer(
+            new page_load_metrics::ResourceTrackingPageLoadMetricsObserver());
+    // Keep track of the observer pointer so we can check it in the unit test.
+    observer_ = observer.get();
+    tracker->AddObserver(std::move(observer));
+  }
+
+  page_load_metrics::ResourceTrackingPageLoadMetricsObserver* observer() {
+    return observer_;
+  }
+
+ private:
+  page_load_metrics::ResourceTrackingPageLoadMetricsObserver* observer_;

[Bryan McQuade, 2017/04/24 13:56:55]

can you add a comment noting that the observer is owned by the last created
PageLoadTracker and its lifetime is dictated by that tracker's lifetime?

[Pete Williamson, 2017/04/24 19:53:14]

Done.

+};
+
+TEST_F(ResourceTrackingPageLoadMetricsObserverTest, StartAndFinish) {
+  page_load_metrics::ExtraRequestStartInfo start_info_1{
+      content::ResourceType::RESOURCE_TYPE_IMAGE};
+
+  page_load_metrics::ExtraRequestStartInfo start_info_2{
+      content::ResourceType::RESOURCE_TYPE_IMAGE};
+
+  page_load_metrics::ExtraRequestCompleteInfo done_info = {
+      false /*was_cached*/, 1024 * 40 /* raw_body_bytes */,
+      false /* data_reduction_proxy_used*/,
+      1024 * 40 /* original_network_content_length */,
+      content::ResourceType::RESOURCE_TYPE_IMAGE};
+
+  // Start the navigation. This will create the page load tracker and register
+  // the observers.
+  NavigateAndCommit(GURL(kFakeUrl));
+
+  // Simulate starting two images, and completing one.
+  SimulateStartedResource(start_info_1);
+  SimulateStartedResource(start_info_2);
+  SimulateLoadedResource(done_info);
+
+  int64_t started = -1;
+  int64_t completed = -1;
+  EXPECT_NE(nullptr, observer());
+  observer()->GetCountsForTypeForTesting(
+      content::ResourceType::RESOURCE_TYPE_IMAGE, &started, &completed);
+  EXPECT_EQ(2, started);
+  EXPECT_EQ(1, completed);
+}
+
+}  // namespace page_load_metrics