Remove redundant reading and writing of data about SharedBuffer.

third_party/WebKit/Source/platform/graphics/DecodingImageGenerator.cpp

Index: third_party/WebKit/Source/platform/graphics/DecodingImageGenerator.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/DecodingImageGenerator.cpp b/third_party/WebKit/Source/platform/graphics/DecodingImageGenerator.cpp
index 88ac3e771e05cb8f64908183d9df2afa248f1885..a1e195ba7d9dc211655f9815ddf0b11e28505248 100644
--- a/third_party/WebKit/Source/platform/graphics/DecodingImageGenerator.cpp
+++ b/third_party/WebKit/Source/platform/graphics/DecodingImageGenerator.cpp
@@ -27,6 +27,7 @@
 
 #include <memory>
 #include "platform/SharedBuffer.h"
+#include "platform/SharedBufferStep.h"
 #include "platform/graphics/ImageFrameGenerator.h"
 #include "platform/image-decoders/ImageDecoder.h"
 #include "platform/image-decoders/SegmentReader.h"
@@ -39,19 +40,42 @@ namespace blink {
 DecodingImageGenerator::DecodingImageGenerator(
     PassRefPtr<ImageFrameGenerator> frame_generator,
     const SkImageInfo& info,
-    PassRefPtr<SegmentReader> data,
+    PassRefPtr<SegmentReader> reader,
     bool all_data_received,
     size_t index,
     uint32_t unique_id)
     : SkImageGenerator(info, unique_id),
       frame_generator_(std::move(frame_generator)),
-      data_(std::move(data)),
+      reader_(std::move(reader)),
+      all_data_received_(all_data_received),
+      frame_index_(index),
+      can_yuv_decode_(false) {}
+
+DecodingImageGenerator::DecodingImageGenerator(
+    PassRefPtr<ImageFrameGenerator> frame_generator,
+    const SkImageInfo& info,
+    PassRefPtr<SharedBuffer::ThreadSafeStepper> stepper,
+    bool all_data_received,
+    size_t index,
+    uint32_t unique_id)
+    : SkImageGenerator(info, unique_id),
+      frame_generator_(std::move(frame_generator)),
+      stepper_(std::move(stepper)),
       all_data_received_(all_data_received),
       frame_index_(index),
       can_yuv_decode_(false) {}
 
 DecodingImageGenerator::~DecodingImageGenerator() {}
 
+PassRefPtr<SegmentReader> DecodingImageGenerator::encoded_data() const {
+  if (reader_) {
+    return reader_;
+  }
+
+  RefPtr<SharedBufferStep> step = stepper_->current_step();
+  return SegmentReader::CreateFromSharedBufferStep(step);
+}
+
 SkData* DecodingImageGenerator::onRefEncodedData() {
   TRACE_EVENT0("blink", "DecodingImageGenerator::refEncodedData");
 
@@ -59,7 +83,7 @@ SkData* DecodingImageGenerator::onRefEncodedData() {
   // serializers, which want the data even if it requires copying, and even
   // if the data is incomplete. (Otherwise they would potentially need to
   // decode the partial image in order to re-encode it.)
-  return data_->GetAsSkData().release();
+  return encoded_data()->GetAsSkData().release();
 }
 
 bool DecodingImageGenerator::onGetPixels(const SkImageInfo& dst_info,
@@ -100,8 +124,9 @@ bool DecodingImageGenerator::onGetPixels(const SkImageInfo& dst_info,
   }
 
   PlatformInstrumentation::WillDecodeLazyPixelRef(uniqueID());
-  const bool decoded = frame_generator_->DecodeAndScale(
-      data_.Get(), all_data_received_, frame_index_, decode_info, pixels,
+  RefPtr<SegmentReader> data = encoded_data();
+  bool decoded = frame_generator_->DecodeAndScale(
+      data.Get(), all_data_received_, frame_index_, decode_info, pixels,
       row_bytes, alpha_option);
   PlatformInstrumentation::DidDecodeLazyPixelRef();
 
@@ -132,7 +157,8 @@ bool DecodingImageGenerator::onQueryYUV8(SkYUVSizeInfo* size_info,
   if (color_space)
     *color_space = kJPEG_SkYUVColorSpace;
 
-  return frame_generator_->GetYUVComponentSizes(data_.Get(), size_info);
+  RefPtr<SegmentReader> data = encoded_data();
+  return frame_generator_->GetYUVComponentSizes(data.Get(), size_info);
 }
 
 bool DecodingImageGenerator::onGetYUV8Planes(const SkYUVSizeInfo& size_info,
@@ -146,8 +172,9 @@ bool DecodingImageGenerator::onGetYUV8Planes(const SkYUVSizeInfo& size_info,
                static_cast<int>(frame_index_));
 
   PlatformInstrumentation::WillDecodeLazyPixelRef(uniqueID());
+  RefPtr<SegmentReader> data = encoded_data();
   bool decoded =
-      frame_generator_->DecodeToYUV(data_.Get(), frame_index_, size_info.fSizes,
+      frame_generator_->DecodeToYUV(data.Get(), frame_index_, size_info.fSizes,
                                     planes, size_info.fWidthBytes);
   PlatformInstrumentation::DidDecodeLazyPixelRef();