[page_load_metrics] Add support for chrome:// urls and add extensions observer

chrome/browser/page_load_metrics/page_load_metrics_browsertest.cc

 // Copyright (c) 2015 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 "base/macros.h"
 #include "base/test/histogram_tester.h"
 #include "base/time/time.h"
 #include "chrome/browser/page_load_metrics/metrics_web_contents_observer.h"
 #include "chrome/browser/page_load_metrics/observers/aborts_page_load_metrics_observer.h"
 #include "chrome/browser/page_load_metrics/observers/core_page_load_metrics_observer.h"
 #include "chrome/browser/page_load_metrics/observers/document_write_page_load_metrics_observer.h"
 #include "chrome/browser/page_load_metrics/observers/no_state_prefetch_page_load_metrics_observer.h"
+#include "chrome/browser/page_load_metrics/observers/webui_page_load_metrics_observer.h"
 #include "chrome/browser/prerender/prerender_histograms.h"
 #include "chrome/browser/prerender/prerender_origin.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_navigator_params.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
 #include "chrome/common/url_constants.h"
 #include "chrome/test/base/in_process_browser_test.h"
 #include "chrome/test/base/ui_test_utils.h"
 #include "content/public/browser/browser_thread.h"
@@ skipping 250 matching lines @@
 
   ui_test_utils::NavigateToURL(
       browser(), embedded_test_server()->GetURL(
                      "/page_load_metrics/document_write_no_script.html"));
   NavigateToUntrackedUrl();
 
   histogram_tester_.ExpectTotalCount(
       internal::kHistogramDocWriteBlockParseStartToFirstContentfulPaint, 0);
 }
 
+IN_PROC_BROWSER_TEST_F(PageLoadMetricsBrowserTest, ExtensionsPage) {
+  ASSERT_TRUE(embedded_test_server()->Start());
+  ui_test_utils::NavigateToURL(browser(), GURL("chrome://extensions"));
+  NavigateToUntrackedUrl();
+  histogram_tester_.ExpectTotalCount(
+      internal::kHistogramExtensionsParseDuration, 1);
+}
+
+IN_PROC_BROWSER_TEST_F(PageLoadMetricsBrowserTest, ExtensionsPageAbout) {
+  ASSERT_TRUE(embedded_test_server()->Start());
+  ui_test_utils::NavigateToURL(browser(), GURL("about:extensions"));
+  NavigateToUntrackedUrl();
+  histogram_tester_.ExpectTotalCount(
+      internal::kHistogramExtensionsParseDuration, 1);
+}
+
 IN_PROC_BROWSER_TEST_F(PageLoadMetricsBrowserTest, BadXhtml) {
   ASSERT_TRUE(embedded_test_server()->Start());
 
   // When an XHTML page contains invalid XML, it causes a paint of the error
   // message without a layout. Page load metrics currently treats this as an
   // error. Eventually, we'll fix this by special casing the handling of
   // documents with non-well-formed XML on the blink side. See crbug.com/627607
   // for more.
   ui_test_utils::NavigateToURL(
       browser(),
@@ skipping 211 matching lines @@
 
   histogram_tester_.ExpectTotalCount(
       prerender::PrerenderHistograms::GetFirstContentfulPaintHistogramName(
           prerender::ORIGIN_NONE, false, true, base::TimeDelta()),
       1);
   histogram_tester_.ExpectTotalCount(
       prerender::PrerenderHistograms::GetFirstContentfulPaintHistogramName(
           prerender::ORIGIN_NONE, false, false, base::TimeDelta()),
       0);
 }