Remove redundant reading and writing of data about SharedBuffer.

third_party/WebKit/Source/platform/image-decoders/SegmentReader.cpp

Index: third_party/WebKit/Source/platform/image-decoders/SegmentReader.cpp
diff --git a/third_party/WebKit/Source/platform/image-decoders/SegmentReader.cpp b/third_party/WebKit/Source/platform/image-decoders/SegmentReader.cpp
index f40f5e70697d4d9a2a60cf0c49a2f9d151e856fd..113296cd1214f99e3af049034963094040a5bce0 100644
--- a/third_party/WebKit/Source/platform/image-decoders/SegmentReader.cpp
+++ b/third_party/WebKit/Source/platform/image-decoders/SegmentReader.cpp
@@ -5,6 +5,7 @@
 #include "platform/image-decoders/SegmentReader.h"
 
 #include "platform/SharedBuffer.h"
+#include "platform/SharedBufferStep.h"
 #include "platform/wtf/Assertions.h"
 #include "platform/wtf/Noncopyable.h"
 #include "platform/wtf/PassRefPtr.h"
@@ -47,6 +48,41 @@ sk_sp<SkData> SharedBufferSegmentReader::GetAsSkData() const {
   return shared_buffer_->GetAsSkData();
 }
 
+// SharedBufferStepSegmentReader
+// ---------------------------------------------------
+
+// Interface for ImageDecoder to read a SharedBufferStep.
+class SharedBufferStepSegmentReader final : public SegmentReader {
+  WTF_MAKE_NONCOPYABLE(SharedBufferStepSegmentReader);
+
+ public:
+  SharedBufferStepSegmentReader(PassRefPtr<SharedBufferStep>);
+  size_t size() const override;
+  size_t GetSomeData(const char*& data, size_t position) const override;
+  sk_sp<SkData> GetAsSkData() const override;
+
+ private:
+  RefPtr<SharedBufferStep> step_;
+  size_t size_;
+};
+
+SharedBufferStepSegmentReader::SharedBufferStepSegmentReader(
+    PassRefPtr<SharedBufferStep> step)
+    : step_(std::move(step)), size_(step_->size()) {}
+
+size_t SharedBufferStepSegmentReader::size() const {
+  return size_;
+}
+
+size_t SharedBufferStepSegmentReader::GetSomeData(const char*& data,
+                                                  size_t position) const {
+  return step_->GetSomeData(data, position);
+}
+
+sk_sp<SkData> SharedBufferStepSegmentReader::GetAsSkData() const {
+  return step_->GetAsSkData();
+}
+
 // DataSegmentReader -----------------------------------------------------------
 
 // Interface for ImageDecoder to read an SkData.
@@ -190,6 +226,11 @@ PassRefPtr<SegmentReader> SegmentReader::CreateFromSkData(sk_sp<SkData> data) {
   return AdoptRef(new DataSegmentReader(std::move(data)));
 }
 
+PassRefPtr<SegmentReader> SegmentReader::CreateFromSharedBufferStep(
+    PassRefPtr<SharedBufferStep> step) {
+  return AdoptRef(new SharedBufferStepSegmentReader(std::move(step)));
+}
+
 PassRefPtr<SegmentReader> SegmentReader::CreateFromSkROBuffer(
     sk_sp<SkROBuffer> buffer) {
   return AdoptRef(new ROBufferSegmentReader(std::move(buffer)));