Fill incomplete images in SkCodec parent class

src/codec/SkWebpCodec.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 "SkCodecPriv.h"
 #include "SkWebpCodec.h"
 #include "SkTemplates.h"
@@ skipping 133 matching lines @@
 
     // As stated below, libwebp snaps to even left and top. Make sure top and left are even, so we
     // decode this exact subset.
     // Leave right and bottom unmodified, so we suggest a slightly larger subset than requested.
     desiredSubset->fLeft = (desiredSubset->fLeft >> 1) << 1;
     desiredSubset->fTop = (desiredSubset->fTop >> 1) << 1;
     return true;
 }
 
 SkCodec::Result SkWebpCodec::onGetPixels(const SkImageInfo& dstInfo, void* dst, size_t rowBytes,
-                                         const Options& options, SkPMColor*, int*) {
+                                         const Options& options, SkPMColor*, int*,
+                                         int* incompleteScanlines) {
     if (!this->rewindIfNeeded()) {
         return kCouldNotRewind;
     }
 
     if (!webp_conversion_possible(dstInfo, this->getInfo())) {
         return kInvalidConversion;
     }
 
     WebPDecoderConfig config;
     if (0 == WebPInitDecoderConfig(&config)) {
@@ skipping 59 matching lines @@
     SkAutoTCallVProc<WebPIDecoder, WebPIDelete> idec(WebPIDecode(nullptr, 0, &config));
     if (!idec) {
         return kInvalidInput;
     }
 
     SkAutoMalloc storage(BUFFER_SIZE);
     uint8_t* buffer = static_cast<uint8_t*>(storage.get());
     while (true) {
         const size_t bytesRead = stream()->read(buffer, BUFFER_SIZE);
         if (0 == bytesRead) {
-            // FIXME: Maybe this is an incomplete image? How to decide? Based
-            // on the number of rows decoded? We can know the number of rows
-            // decoded using WebPIDecGetRGB.
-            return kInvalidInput;
+            int rowsDecoded;
+            WebPIDecGetRGB(idec, &rowsDecoded, NULL, NULL, NULL);
+            *incompleteScanlines = dstDimensions.height() - rowsDecoded;
+            return kIncompleteInput;
         }
 
         switch (WebPIAppend(idec, buffer, bytesRead)) {
             case VP8_STATUS_OK:
                 return kSuccess;
             case VP8_STATUS_SUSPENDED:
                 // Break out of the switch statement. Continue the loop.
                 break;
             default:
                 return kInvalidInput;
         }
     }
 }
 
 SkWebpCodec::SkWebpCodec(const SkImageInfo& info, SkStream* stream)
     : INHERITED(info, stream) {}