Define a variable to distinguish system_icu from bundled_icu in Blink

Source/wtf/text/TextCodecICU.h

Index: Source/wtf/text/TextCodecICU.h
diff --git a/Source/wtf/text/TextCodecICU.h b/Source/wtf/text/TextCodecICU.h
index d11f0ad10701d71b5f7ffb841f5d8b4168ca360f..b3e6e8d7b6844e64c0720b52223c7cac30dafa9b 100644
--- a/Source/wtf/text/TextCodecICU.h
+++ b/Source/wtf/text/TextCodecICU.h
@@ -58,15 +58,19 @@ private:
 
     void createICUConverter() const;
     void releaseICUConverter() const;
+#if defined(USING_SYSTEM_ICU)
     bool needsGBKFallbacks() const { return m_needsGBKFallbacks; }
     void setNeedsGBKFallbacks(bool needsFallbacks) { m_needsGBKFallbacks = needsFallbacks; }
+#endif
 
     int decodeToBuffer(UChar* buffer, UChar* bufferLimit, const char*& source,
         const char* sourceLimit, int32_t* offsets, bool flush, UErrorCode&);
 
     TextEncoding m_encoding;
     mutable UConverter* m_converterICU;
+#if defined(USING_SYSTEM_ICU)
     mutable bool m_needsGBKFallbacks;
+#endif
 };
 
 struct ICUConverterWrapper {