Fix virtual/override/final usage in Source/platform/.

Source/platform/image-decoders/gif/GIFImageDecoder.h

Index: Source/platform/image-decoders/gif/GIFImageDecoder.h
diff --git a/Source/platform/image-decoders/gif/GIFImageDecoder.h b/Source/platform/image-decoders/gif/GIFImageDecoder.h
index e969e89899e93e3a80b556b50129599feaf27064..d4c25f1775e3aa86f766fbe0ad04efa90196fffd 100644
--- a/Source/platform/image-decoders/gif/GIFImageDecoder.h
+++ b/Source/platform/image-decoders/gif/GIFImageDecoder.h
@@ -41,21 +41,21 @@ class PLATFORM_EXPORT GIFImageDecoder : public ImageDecoder {
     WTF_MAKE_NONCOPYABLE(GIFImageDecoder);
 public:
     GIFImageDecoder(ImageSource::AlphaOption, ImageSource::GammaAndColorProfileOption, size_t maxDecodedBytes);
-    virtual ~GIFImageDecoder();
+    ~GIFImageDecoder() override;
 
     enum GIFParseQuery { GIFSizeQuery, GIFFrameCountQuery };
 
     // ImageDecoder:
-    virtual String filenameExtension() const override { return "gif"; }
-    virtual void setData(SharedBuffer* data, bool allDataReceived) override;
-    virtual int repetitionCount() const override;
-    virtual bool frameIsCompleteAtIndex(size_t) const override;
-    virtual float frameDurationAtIndex(size_t) const override;
-    virtual size_t clearCacheExceptFrame(size_t) override;
+    String filenameExtension() const override { return "gif"; }
+    void setData(SharedBuffer* data, bool allDataReceived) override;
+    int repetitionCount() const override;
+    bool frameIsCompleteAtIndex(size_t) const override;
+    float frameDurationAtIndex(size_t) const override;
+    size_t clearCacheExceptFrame(size_t) override;
     // CAUTION: setFailed() deletes |m_reader|.  Be careful to avoid
     // accessing deleted memory, especially when calling this from inside
     // GIFImageReader!
-    virtual bool setFailed() override;
+    bool setFailed() override;
 
     // Callbacks from the GIF reader.
     bool haveDecodedRow(size_t frameIndex, GIFRow::const_iterator rowBegin, size_t width, size_t rowNumber, unsigned repeatCount, bool writeTransparentPixels);
@@ -66,11 +66,11 @@ public:
 
 private:
     // ImageDecoder:
-    virtual void clearFrameBuffer(size_t frameIndex) override;
+    void clearFrameBuffer(size_t frameIndex) override;
     virtual void decodeSize() { parse(GIFSizeQuery); }
-    virtual size_t decodeFrameCount() override;
-    virtual void initializeNewFrame(size_t) override;
-    virtual void decode(size_t) override;
+    size_t decodeFrameCount() override;
+    void initializeNewFrame(size_t) override;
+    void decode(size_t) override;
 
     // Parses as much as is needed to answer the query, ignoring bitmap
     // data. If parsing fails, sets the "decode failure" flag.