Split TLS implementation into its own translation unit.

src/ports/SkTLS_pthread.cpp

+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkTLS.h"
+
+#include <pthread.h>
+
+static pthread_key_t gSkTLSKey;
+static pthread_once_t gSkTLSKey_Once = PTHREAD_ONCE_INIT;
+
+static void sk_tls_make_key() {
+    (void)pthread_key_create(&gSkTLSKey, SkTLS::Destructor);
+}
+
+void* SkTLS::PlatformGetSpecific(bool forceCreateTheSlot) {
+    // should we use forceCreateTheSlot to potentially skip calling pthread_once
+    // and just return NULL if we've never been called with
+    // forceCreateTheSlot==true ?
+
+    (void)pthread_once(&gSkTLSKey_Once, sk_tls_make_key);
+    return pthread_getspecific(gSkTLSKey);
+}
+
+void SkTLS::PlatformSetSpecific(void* ptr) {
+    (void)pthread_setspecific(gSkTLSKey, ptr);
+}