Add SkSpecialImage::extractSubset & NewFromPixmap

tests/Float16Test.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Test.h"
+#include "SkAutoPixmapStorage.h"
 #include "SkColor.h"
 #include "SkHalf.h"
 #include "SkOpts.h"
 #include "SkPixmap.h"
 #include "SkPM4f.h"
 #include "SkRandom.h"
 
 static bool eq_within_half_float(float a, float b) {
     const float kTolerance = 1.0f / (1 << (8 + 10));
 
@@ skipping 87 matching lines @@
             bool ok = (h1 == h2 || h1 == h2-1);
             REPORTER_ASSERT(r, ok);
             if (!ok) {
                 SkDebugf("%08x (%d) -> %04x (%d), want %04x (%d)\n",
                          bits, bits>>23, h1, h1>>10, h2, h2>>10);
                 break;
             }
         }
     }
 }