Clean up a few includes, introduce iwyu.

src/ports/SkDebug_stdio.cpp

-
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
-
 #include "SkTypes.h"
 
 #include <stdarg.h>
 #include <stdio.h>
 
-void SkDebugf(const char format[], ...) {
+SK_API void SkDebugf(const char format[], ...) {

[bungeman-skia, 2015/06/25 15:11:34]

This make iwyu happy, but definitions can't have this, only delarations. I'll
have to see what's really going on.

[bungeman-skia, 2015/06/25 20:38:46]

Forget what I said before, this makes iwyu happy because SK_API is in SkTypes.h.
What seems to be really going on is this: iwyu currently makes no distinction
between declarations and definitions. As a result, it will never try to keep a
header just because it declares a function which the current file is defining.
It sometimes seems like it's doing this due to special casing of foo.cc and
foo.h (associated headers), but it actually isn't.

In some sense this is 'correct' in that there is technically no need to forward
declare a function being defined (the forward declaration isn't being 'used').
On the other hand there are warnings in the compiler about having extern
functions without a prior declaration. As a result, I believe iwyu's opinion
here is quite backwards. I would actually prefer that it suggest directly
including at least one header which declares each extern function. In other
words, the forward declaration is a 'use' because any (extern) definition
without a declaration would be an error.

[bungeman-skia, 2015/06/25 21:27:26]

The compiler warning I was referring to turns out to be called
-Wmissing-declarations . This warning does catch removing SkTypes.h from this
file.

     va_list args;
     va_start(args, format);
     vfprintf(stderr, format, args);
     va_end(args);
 }