Consolidate SkCodec functions for handling rewind

src/codec/SkCodec_libgif.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 "SkCodec_libgif.h"
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
@@ skipping 216 matching lines @@
             return kPremul_SkAlphaType == dst.alphaType() ||
                     kUnpremul_SkAlphaType == dst.alphaType();
         case kIndex_8_SkColorType:
             return kPremul_SkAlphaType == dst.alphaType() ||
                     kUnpremul_SkAlphaType == dst.alphaType();
         default:
             return false;
     }
 }
 
+bool SkGifCodec::onRewind() {
+    GifFileType* gifOut = NULL;
+    if (!ReadHeader(this->stream(), NULL, &gifOut)) {
+        return false;
+    }
+
+    SkASSERT(NULL != gifOut);
+    fGif.reset(gifOut);
+    return true;
+}
+
 /*
  * Initiates the gif decode
  */
 SkCodec::Result SkGifCodec::onGetPixels(const SkImageInfo& dstInfo,
                                         void* dst, size_t dstRowBytes,
                                         const Options& opts,
                                         SkPMColor* inputColorPtr,
                                         int* inputColorCount) {
     // Rewind if necessary
-    SkCodec::RewindState rewindState = this->rewindIfNeeded();
-    if (rewindState == kCouldNotRewind_RewindState) {
+    if (!this->rewindIfNeeded()) {
         return kCouldNotRewind;
-    } else if (rewindState == kRewound_RewindState) {
-        GifFileType* gifOut = NULL;
-        if (!ReadHeader(this->stream(), NULL, &gifOut)) {
-            return kCouldNotRewind;
-        } else {
-            SkASSERT(NULL != gifOut);
-            fGif.reset(gifOut);
-        }
     }
 
     // Check for valid input parameters
     if (opts.fSubset) {
         // Subsets are not supported.
         return kUnimplemented;
     }
     if (dstInfo.dimensions() != this->getInfo().dimensions()) {
         return gif_error("Scaling not supported.\n", kInvalidScale);
     }
@@ skipping 304 matching lines @@
                 // giflib returns an error code if the record type is not known.
                 // We should catch this error immediately.
                 SkASSERT(false);
                 break;
         }
     } while (TERMINATE_RECORD_TYPE != recordType);
 
     return gif_error("Could not find any images to decode in gif file.\n",
             kInvalidInput);
 }