Add immediate variants of doc.write page load metrics

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 "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/test/base/in_process_browser_test.h"
 #include "chrome/test/base/ui_test_utils.h"
@@ skipping 118 matching lines @@
       browser(), embedded_test_server()->GetURL(
                      "/page_load_metrics/document_write_script_block.html"));
 
   ui_test_utils::NavigateToURL(
       browser(), embedded_test_server()->GetURL(
                      "/page_load_metrics/document_write_script_block.html"));
 
   histogram_tester_.ExpectTotalCount(
       internal::kHistogramDocWriteBlockParseStartToFirstContentfulPaint, 1);
 
-  histogram_tester_.ExpectTotalCount(
-      internal::kHistogramDocWriteBlockReloadCount, 1);
-
   ui_test_utils::NavigateToURL(browser(),
                                embedded_test_server()->GetURL("/title2.html"));
 
   histogram_tester_.ExpectTotalCount(
       internal::kHistogramDocWriteBlockParseStartToFirstContentfulPaint, 1);
 
+  // Testing this histogram's value only in the end else the test will be

[Bryan McQuade, 2016/06/17 13:24:03]

yeah, i had encountered similar issues with timing races in this test. i think
you can remove this comment. it's useful for the code reviewer but i don't know
it'll be useful for readers of the code once this patch is committed.

+  // dependent on IPC timing.
   histogram_tester_.ExpectTotalCount(
       internal::kHistogramDocWriteBlockReloadCount, 2);
 }
 
 IN_PROC_BROWSER_TEST_F(MetricsWebContentsObserverBrowserTest,
                        DocumentWriteASync) {
   ASSERT_TRUE(embedded_test_server()->Start());
 
   ui_test_utils::NavigateToURL(
       browser(), embedded_test_server()->GetURL(
@@ skipping 25 matching lines @@
 
   ui_test_utils::NavigateToURL(
       browser(), embedded_test_server()->GetURL(
                      "/page_load_metrics/document_write_no_script.html"));
   ui_test_utils::NavigateToURL(browser(),
                                embedded_test_server()->GetURL("/title2.html"));
 
   histogram_tester_.ExpectTotalCount(
       internal::kHistogramDocWriteBlockParseStartToFirstContentfulPaint, 0);
 }