Handle SkStream::rewind properly.

src/images/SkImageDecoder_libwebp.cpp

 /*
  * Copyright 2010, The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
@@ skipping 181 matching lines @@
 
 // Incremental WebP image decoding. Reads input buffer of 64K size iteratively
 // and decodes this block to appropriate color-space as per config object.
 static bool webp_idecode(SkStream* stream, WebPDecoderConfig* config) {
     WebPIDecoder* idec = WebPIDecode(NULL, 0, config);
     if (NULL == idec) {
         WebPFreeDecBuffer(&config->output);
         return false;
     }
 
-    stream->rewind();
+    if (!stream->rewind()) {
+        SkDebugf("Failed to rewind webp stream!");
+        return false;
+    }
     const size_t readBufferSize = stream->hasLength() ?
             SkTMin(stream->getLength(), WEBP_IDECODE_BUFFER_SZ) : WEBP_IDECODE_BUFFER_SZ;
     SkAutoMalloc srcStorage(readBufferSize);
     unsigned char* input = (uint8_t*)srcStorage.get();
     if (NULL == input) {
         WebPIDelete(idec);
         WebPFreeDecBuffer(&config->output);
         return false;
     }
 
@@ skipping 91 matching lines @@
     return true;
 }
 
 bool SkWEBPImageDecoder::onBuildTileIndex(SkStream* stream,
                                           int *width, int *height) {
     int origWidth, origHeight, hasAlpha;
     if (!webp_parse_header(stream, &origWidth, &origHeight, &hasAlpha)) {
         return false;
     }
 
-    stream->rewind();
+    if (!stream->rewind()) {
+        SkDebugf("Failed to rewind webp stream!");
+        return false;
+    }
+
     *width = origWidth;
     *height = origHeight;
 
     SkRefCnt_SafeAssign(this->fInputStream, stream);
     this->fOrigWidth = origWidth;
     this->fOrigHeight = origHeight;
     this->fHasAlpha = hasAlpha;
 
     return true;
 }
@@ skipping 270 matching lines @@
     return SkImageDecoder::kUnknown_Format;
 }
 
 static SkImageEncoder* sk_libwebp_efactory(SkImageEncoder::Type t) {
       return (SkImageEncoder::kWEBP_Type == t) ? SkNEW(SkWEBPImageEncoder) : NULL;
 }
 
 static SkTRegistry<SkImageDecoder*, SkStream*> gDReg(sk_libwebp_dfactory);
 static SkTRegistry<SkImageDecoder::Format, SkStream*> gFormatReg(get_format_webp);
 static SkTRegistry<SkImageEncoder*, SkImageEncoder::Type> gEReg(sk_libwebp_efactory);