Add an option on SkImageDecoder to skip writing 0s.

src/images/SkImageDecoder_libjpeg.cpp

 /*
  * Copyright 2007 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 "SkImageDecoder.h"
 #include "SkImageEncoder.h"
@@ skipping 570 matching lines @@
     } else if (JCS_RGB_565 == cinfo.out_color_space) {
         sc = SkScaledBitmapSampler::kRGB_565;
 #endif
     } else if (1 == cinfo.out_color_components &&
                JCS_GRAYSCALE == cinfo.out_color_space) {
         sc = SkScaledBitmapSampler::kGray;
     } else {
         return return_false(cinfo, *bm, "jpeg colorspace");
     }
 
-    if (!sampler.begin(bm, sc, this->getDitherImage())) {
+    if (!sampler.begin(bm, sc, *this)) {
         return return_false(cinfo, *bm, "sampler.begin");
     }
 
     // The CMYK work-around relies on 4 components per pixel here
     SkAutoMalloc srcStorage(cinfo.output_width * 4);
     uint8_t* srcRow = (uint8_t*)srcStorage.get();
 
     //  Possibly skip initial rows [sampler.srcY0]
     if (!skip_src_rows(&cinfo, srcRow, sampler.srcY0())) {
         return return_false(cinfo, *bm, "skip rows");
@@ skipping 218 matching lines @@
     } else if (JCS_RGB_565 == cinfo->out_color_space) {
         sc = SkScaledBitmapSampler::kRGB_565;
 #endif
     } else if (1 == cinfo->out_color_components &&
                JCS_GRAYSCALE == cinfo->out_color_space) {
         sc = SkScaledBitmapSampler::kGray;
     } else {
         return return_false(*cinfo, *bm, "jpeg colorspace");
     }
 
-    if (!sampler.begin(&bitmap, sc, this->getDitherImage())) {
+    if (!sampler.begin(&bitmap, sc, *this)) {
         return return_false(*cinfo, bitmap, "sampler.begin");
     }
 
     // The CMYK work-around relies on 4 components per pixel here
     SkAutoMalloc  srcStorage(width * 4);
     uint8_t* srcRow = (uint8_t*)srcStorage.get();
 
     //  Possibly skip initial rows [sampler.srcY0]
     if (!skip_src_rows_tile(cinfo, fImageIndex->huffmanIndex(), srcRow, sampler.srcY0())) {
         return return_false(*cinfo, bitmap, "skip rows");
@@ skipping 311 matching lines @@
     return SkImageDecoder::kUnknown_Format;
 }
 
 static SkImageEncoder* sk_libjpeg_efactory(SkImageEncoder::Type t) {
     return (SkImageEncoder::kJPEG_Type == t) ? SkNEW(SkJPEGImageEncoder) : NULL;
 }
 
 static SkImageDecoder_DecodeReg gDReg(sk_libjpeg_dfactory);
 static SkImageDecoder_FormatReg gFormatReg(get_format_jpeg);
 static SkImageEncoder_EncodeReg gEReg(sk_libjpeg_efactory);