Clean up a few includes, introduce iwyu.

src/ports/SkGlobalInitialization_default.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
-#include "SkTypes.h"
-
 #include "SkBitmapProcShader.h"
-#include "SkMallocPixelRef.h"
 #include "SkPathEffect.h"
-#include "SkPixelRef.h"
 #include "SkXfermode.h"
 
 #include "Sk1DPathEffect.h"
 #include "Sk2DPathEffect.h"
 #include "SkArithmeticMode.h"
 #include "SkArcToPathEffect.h"
 #include "SkBitmapSource.h"
 #include "SkBlurDrawLooper.h"
 #include "SkBlurImageFilter.h"
 #include "SkBlurMaskFilter.h"
@@ skipping 93 matching lines @@
         SkLightingImageFilter::InitializeFlattenables();
         SkTableColorFilter::InitializeFlattenables();
         SkXfermode::InitializeFlattenables();
     }
 };
 
 SK_DECLARE_STATIC_ONCE(once);
 void SkFlattenable::InitializeFlattenablesIfNeeded() {
     SkOnce(&once, SkPrivateEffectInitializer::Init);
 }