Add thread safety configuration check.

include/utils/SkCondVar.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkCondVar_DEFINED
 #define SkCondVar_DEFINED
 
+/**
+ * Import any thread model setting from configuration files.

[reed1, 2014/07/08 13:19:55]

Does this comment belong here, or above <pthread.h> ?

[scroggo, 2014/07/08 13:23:44]

The include of SkTypes.h is to make sure that SK_USE_POSIX_THREADS or
SK_BUILD_FOR_WIN32 is appropriately defined. I think this is the right place for
a comment (although perhaps the comment is not clear enough?).

+ */
+#include "SkTypes.h"
+
 #ifdef SK_USE_POSIX_THREADS
 #include <pthread.h>
 #elif defined(SK_BUILD_FOR_WIN32)
 #include <windows.h>
+#else
+/**
+ * Warn if the implementation of this class is empty, i.e. thread safety is not working.
+ */
+#warning "Thread safety class SkCondVar has no implementation!"
 #endif
 
 /**
  * Condition variable for blocking access to shared data from other threads and
  * controlling which threads are awake.
  *
  * Currently only supported on platforms with posix threads and Windows Vista and
  * above.
  */
 class SkCondVar {
@@ skipping 34 matching lines @@
 #ifdef SK_USE_POSIX_THREADS
     pthread_mutex_t  fMutex;
     pthread_cond_t   fCond;
 #elif defined(SK_BUILD_FOR_WIN32)
     CRITICAL_SECTION   fCriticalSection;
     CONDITION_VARIABLE fCondition;
 #endif
 };
 
 #endif