Fix the compile errors in image-decoders

In preparation for moving this code to components/, fix the compiler
errors when they are compiled as new files.

- error: [chromium-style] Classes that are ref-counted should have destructors that are declared protected or private.

-error: [chromium-style] virtual methods with non-empty bodies shouldn't be declared inline.

Bug: 1462922
Change-Id: Ic7540f67c88cbd6b41be0810a5f93c5c73cf2b5b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4795549
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1185483}

third_party/blink/renderer/platform/image-decoders/image_decoder.cc

@@ -492,6 +492,10 @@ absl::optional<gfx::HDRMetadata> ImageDecoder::GetHDRMetadata() const {
   return absl::nullopt;
 }
 
+gfx::Size ImageDecoder::FrameSizeAtIndex(wtf_size_t) const {
+  return Size();
+}
+
 cc::ImageHeaderMetadata ImageDecoder::MakeMetadataForDecodeAcceleration()
     const {
   DCHECK(IsDecodedSizeAvailable());

third_party/blink/renderer/platform/image-decoders/image_decoder.h

@@ -310,7 +310,7 @@ class PLATFORM_EXPORT ImageDecoder {
   // sizes. This does NOT differ from Size() for GIF or WebP, since
   // decoding GIF or WebP composites any smaller frames against previous
   // frames to create full-size frames.
-  virtual gfx::Size FrameSizeAtIndex(wtf_size_t) const { return Size(); }
+  virtual gfx::Size FrameSizeAtIndex(wtf_size_t) const;
 
   // Returns whether the size is legal (i.e. not going to result in
   // overflow elsewhere).  If not, marks decoding as failed.

third_party/blink/renderer/platform/image-decoders/segment_reader.h

@@ -49,12 +49,15 @@ class PLATFORM_EXPORT SegmentReader
   SegmentReader() = default;
   SegmentReader(const SegmentReader&) = delete;
   SegmentReader& operator=(const SegmentReader&) = delete;
-  virtual ~SegmentReader() = default;
   virtual size_t size() const = 0;
   virtual size_t GetSomeData(const char*& data, size_t position) const = 0;
   virtual sk_sp<SkData> GetAsSkData() const = 0;
   virtual void LockData() {}
   virtual void UnlockData() {}
+
+ protected:
+  friend class ThreadSafeRefCounted<SegmentReader>;
+  virtual ~SegmentReader() = default;
 };
 
 }  // namespace blink