Add subsetting to SkScanlineDecoder

src/codec/SkBmpRLECodec.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBmpRLECodec.h"
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
@@ skipping 241 matching lines @@
                 // This case should not be reached.  We should catch an invalid
                 // color type when we check that the conversion is possible.
                 SkASSERT(false);
                 break;
         }
     }
 }
 
 SkCodec::Result SkBmpRLECodec::prepareToDecode(const SkImageInfo& dstInfo,
         const SkCodec::Options& options, SkPMColor inputColorPtr[], int* inputColorCount) {
+    // FIXME: Support subsets for scanline decodes.
+    if (options.fSubset) {
+        // Subsets are not supported.
+        return kUnimplemented;
+    }
+
     // Reset fSampleX. If it needs to be a value other than 1, it will get modified by
     // the sampler.
     fSampleX = 1;
     // Create the color table if necessary and prepare the stream for decode
     // Note that if it is non-NULL, inputColorCount will be modified
     if (!this->createColorTable(inputColorCount)) {
         SkCodecPrintf("Error: could not create color table.\n");
         return SkCodec::kInvalidInput;
     }
 
@@ skipping 228 matching lines @@
         fSampler.reset(new SkBmpRLESampler(this));
     }
 
     return fSampler;
 }
 
 int SkBmpRLECodec::setSampleX(int sampleX){
     fSampleX = sampleX;
     return get_scaled_dimension(this->getInfo().width(), sampleX);
 }