Cleanup message_loop.cc

Access kHexRangePrintingFlag through HistogramBase:: and not through instance variable. Accessing through instance variable is also correct, but confusing and can lead to future mistakes, because the variable is in this case null.
BUG=517586

Review URL: https://codereview.chromium.org/1278613003

Cr-Commit-Position: refs/heads/master@{#342304}


CrOS-Libchrome-Original-Commit: 0d2bf13aa9865bb69866033b98fb3b78f8b2dcc7
diff --git a/base/message_loop/message_loop.cc b/base/message_loop/message_loop.cc
index 0ae13cb..4e5594b 100644
--- a/base/message_loop/message_loop.cc
+++ b/base/message_loop/message_loop.cc
@@ -565,7 +565,7 @@
         "MsgLoop:" + thread_name_,
         kLeastNonZeroMessageId, kMaxMessageId,
         kNumberOfDistinctMessagesDisplayed,
-        message_histogram_->kHexRangePrintingFlag,
+        HistogramBase::kHexRangePrintingFlag,
         event_descriptions_);
   }
 #endif