Clean up a few includes, introduce iwyu.

src/ports/SkOSFile_posix.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 "SkOSFile.h"
 
-#include "SkTFitsIn.h"
-#include "SkTypes.h"
-
 #include <dirent.h>
 #include <stdio.h>
+#include <string.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
 
+#include "SkString.h"
+#include "SkTFitsIn.h"
+#include "SkTemplates.h"
+#include "SkTypes.h"
+
 bool sk_exists(const char *path, SkFILE_Flags flags) {
     int mode = F_OK;
     if (flags & kRead_SkFILE_Flag) {
         mode |= R_OK;
     }
     if (flags & kWrite_SkFILE_Flag) {
         mode |= W_OK;
     }
     return (0 == access(path, mode));
 }
@@ skipping 142 matching lines @@
         }
         if (entry) { // we broke out with a file
             if (name) {
                 name->set(entry->d_name);
             }
             return true;
         }
     }
     return false;
 }