Revert of Remove SkThread.h, include SkMutex.h or SkAtomics.h as appropriate.

tools/sk_tool_utils_font.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Resources.h"
 #include "SkFontMgr.h"
-#include "SkMutex.h"
 #include "SkOSFile.h"
 #include "SkTestScalerContext.h"
+#include "SkThread.h"
 #include "SkUtils.h"
 #include "sk_tool_utils.h"
 
 namespace sk_tool_utils {
 
 #include "test_font_monospace.cpp"
 #include "test_font_sans_serif.cpp"
 #include "test_font_serif.cpp"
 #include "test_font_index.cpp"
 
@@ skipping 148 matching lines @@
                 break;
             }
         }
        fprintf(out, ";\n");
     }
     fclose(out);
 }
 #endif
 
 }