Make DUMP_HASHTABLE_STATS* buildable.

clang produces errors for conditional mutex locking in
HashTableStats::recordCollisionAtCount() and
HashTableStats::DumpStats().

> .../wtf/HashTable.cpp:56:7: error: mutex 'hashTableStatsMutex()' is not held on every path through here [-Werror,-Wthread-safety-analysis]
>   if (count > maxCollisions)
>       ^

Avoid such errors by moving lock() and unlock() into a single block.

This CL has no behavior changes.

Change-Id: If64ca5700bda0d881fd96ee84b8115b419a8aa63
Reviewed-on: https://chromium-review.googlesource.com/974667Reviewed-by: Yuta Kitamura <yutak@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545032}

third_party/WebKit/Source/platform/wtf/HashTable.cpp

@@ -49,25 +49,32 @@ void HashTableStats::copy(const HashTableStats* other) {
 
 void HashTableStats::recordCollisionAtCount(int count) {
   // The global hash table singleton needs to be atomically updated.
-  bool isGlobalSingleton = this == &instance();
-  if (isGlobalSingleton)
-    hashTableStatsMutex().lock();
+  if (this == &instance()) {
+    MutexLocker locker(hashTableStatsMutex());
+    RecordCollisionAtCountWithoutLock(count);
+  } else {
+    RecordCollisionAtCountWithoutLock(count);
+  }
+}
 
+void HashTableStats::RecordCollisionAtCountWithoutLock(int count) {
   if (count > maxCollisions)
     maxCollisions = count;
   numCollisions++;
   collisionGraph[count]++;
-
-  if (isGlobalSingleton)
-    hashTableStatsMutex().unlock();
 }
 
 void HashTableStats::DumpStats() {
   // Lock the global hash table singleton while dumping.
-  bool isGlobalSingleton = this == &instance();
-  if (isGlobalSingleton)
-    hashTableStatsMutex().lock();
+  if (this == &instance()) {
+    MutexLocker locker(hashTableStatsMutex());
+    DumpStatsWithoutLock();
+  } else {
+    DumpStatsWithoutLock();
+  }
+}
 
+void HashTableStats::DumpStatsWithoutLock() {
   DeprecatedDataLogF("\nWTF::HashTable statistics\n\n");
   DeprecatedDataLogF("%d accesses\n", numAccesses);
   DeprecatedDataLogF("%d total collisions, average %.2f probes per access\n",
@@ -84,9 +91,6 @@ void HashTableStats::DumpStats() {
   }
   DeprecatedDataLogF("%d rehashes\n", numRehashes);
   DeprecatedDataLogF("%d reinserts\n", numReinserts);
-
-  if (isGlobalSingleton)
-    hashTableStatsMutex().unlock();
 }
 
 }  // namespace WTF

third_party/WebKit/Source/platform/wtf/HashTable.h

@@ -136,6 +136,10 @@ struct WTF_EXPORT HashTableStats {
 
   template <typename VisitorDispatcher>
   void trace(VisitorDispatcher) {}
+
+ private:
+  void RecordCollisionAtCountWithoutLock(int count);
+  void DumpStatsWithoutLock();
 };
 
 #if DUMP_HASHTABLE_STATS_PER_TABLE