Removed errorneous DCHECK from TaskManager SharedSampler code

chrome/browser/task_manager/sampling/shared_sampler_win.cc

 // Copyright 2016 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/task_manager/sampling/shared_sampler.h"
 
 #include <windows.h>
 #include <winternl.h>
 
 #include <algorithm>
@@ skipping 351 matching lines @@
     return;
 
   DCHECK(callbacks_map_.find(process_id) != callbacks_map_.end());
 
   if (refresh_flags_ == 0) {
     base::PostTaskAndReplyWithResult(
         blocking_pool_runner_.get(), FROM_HERE,
         base::Bind(&SharedSampler::RefreshOnWorkerThread, this),
         base::Bind(&SharedSampler::OnRefreshDone, this));
   } else {
+    // http://crbug.com/678471
     // A group of consecutive Refresh calls should all specify the same refresh
-    // flags.
-    DCHECK_EQ(refresh_flags, refresh_flags_);
+    // flags. Rarely RefreshOnWorkerThread could take a long time (> 1 sec),
+    // long enough for a next refresh cycle to start before results are ready
+    // from a previous cycle. In that case refresh_flags_ would still remain
+    // set to the previous cycle refresh flags which might be different than
+    // this cycle refresh flags if a column was added or removed between the two
+    // cycles. The worst that could happen in that condition is that results for
+    // a newly added column would be missing for one extra refresh cycle.
   }
 
   refresh_flags_ |= refresh_flags;
 }
 
 void SharedSampler::ClearState() {
   previous_snapshot_.reset();
 }
 
 std::unique_ptr<SharedSampler::RefreshResults>
@@ skipping 245 matching lines @@
       callback_entry.second.on_physical_memory.Run(physical_bytes);
     }
   }
 
   // Reset refresh_results_ to trigger RefreshOnWorkerThread next time Refresh
   // is called.
   refresh_flags_ = 0;
 }
 
 }  // namespace task_manager