Don't set WTF::Partitions::s_initialized to true before initializing

In theory, a simultaneous caller to Partitions::getBufferPartition()
could see the flag as being true, and return the uninitialized buffer
partition, while another thread is initializing it.

BUG=367672

Review URL: https://codereview.chromium.org/268673012

git-svn-id: svn://svn.chromium.org/blink/trunk@175020 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/wtf/WTF.cpp

@@ -79,8 +79,8 @@ void Partitions::initialize()
     // Guard against two threads hitting here in parallel.
     spinLockLock(&lock);
     if (!s_initialized) {
-        s_initialized = true;
         m_bufferAllocator.init();
+        s_initialized = true;
     }
     spinLockUnlock(&lock);
 }