change write-image to use pipeverbs like everyone else, and add test

src/pipe/SkPipeFormat.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkPipeFormat_DEFINED
 #define SkPipeFormat_DEFINED
 
 #include "SkTypes.h"
 
 #define kDefinePicture_ExtPipeVerb  SkSetFourByteTag('s', 'k', 'p', 'i')
-#define kDefineImage_ExtPipeVerb    SkSetFourByteTag('s', 'k', 'i', 'm')
 
 enum class SkPipeVerb : uint8_t {
     kSave,              // extra == 0
     kSaveLayer,
     kRestore,           // extra == 0
     kConcat,            // extra == SkMatrix::MaskType
     
     kClipRect,          // extra == (SkRegion::Op << 1) | isAntiAlias:1
     kClipRRect,         // extra == (SkRegion::Op << 1) | isAntiAlias:1
     kClipPath,          // extra == (SkRegion::Op << 1) | isAntiAlias:1
@@ skipping 25 matching lines @@
     kDrawVertices,
     
     kDrawPicture,       // extra == picture_index
     kDrawAnnotation,    // extra == (key_len_plus_1:23 << 1) else next 32 | has_data:1
 
     kDefineImage,       // extra == image_index
     kDefineTypeface,
     kDefineFactory,     // extra == factory_index (followed by padded getTypeName string)
     kDefinePicture,     // extra == 0 or forget_index + 1 (0 means we're defining a new picture)
     kEndPicture,        // extra == picture_index
+    kWriteImage,        // extra == image_index
 };
 
 enum PaintUsage {
     kText_PaintUsage        = 1 << 0,
     kTextBlob_PaintUsage    = 1 << 1,
     kGeometry_PaintUsage    = 1 << 2,
     kImage_PaintUsage       = 1 << 3,
     kSaveLayer_PaintUsage   = 1 << 4,
     kDrawPaint_PaintUsage   = 1 << 5,
     kVertices_PaintUsage    = 1 << 6,
@@ skipping 141 matching lines @@
 
 static inline SkPipeVerb unpack_verb(uint32_t data) {
     return (SkPipeVerb)(data >> 24);
 }
 
 static inline unsigned unpack_verb_extra(uint32_t data) {
     return data & 0xFFFFFF;
 }
 
 #endif