Get PageLoadMetricsBrowserTest passing under msan

chrome/browser/page_load_metrics/page_load_metrics_browsertest.cc

 // Copyright 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/files/scoped_temp_dir.h"
 #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"
@@ skipping 128 matching lines @@
 
   void SetTimingUpdatedAndQuit() {
     DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
     matched_timing_update_ = true;
     Quit();
   }
 
   ~TimingUpdatedObserver() override {}
 
   std::unique_ptr<base::RunLoop> run_loop_;
-  int matching_fields_;  // A bitvector composed from ExpectedTimingFields.
+  int matching_fields_ = 0;  // A bitvector composed from ExpectedTimingFields.
   bool matched_timing_update_ = false;
   int match_document_write_block_reload_ = 0;
 };
 
 }  // namespace
 
 class PageLoadMetricsBrowserTest : public InProcessBrowserTest {
  public:
   PageLoadMetricsBrowserTest() {}
   ~PageLoadMetricsBrowserTest() override {}
@@ skipping 583 matching lines @@
   ui_test_utils::NavigateToURL(browser(), embedded_test_server()->GetURL(
                                               "/page_load_metrics/large.html"));
   NavigateToUntrackedUrl();
 
   histogram_tester_.ExpectTotalCount(internal::kHistogramTotalBytes, 1);
 
   // Verify that there is a single sample recorded in the 10kB bucket (the size
   // of the main HTML response).
   histogram_tester_.ExpectBucketCount(internal::kHistogramTotalBytes, 10, 1);
 }