Do not guess UTF8 encoding

third_party/WebKit/Source/platform/text/TextEncodingDetector.cpp

Index: third_party/WebKit/Source/platform/text/TextEncodingDetector.cpp
diff --git a/third_party/WebKit/Source/platform/text/TextEncodingDetector.cpp b/third_party/WebKit/Source/platform/text/TextEncodingDetector.cpp
index a9497c74be0ff92a8233ad4cda8bcdd7f5939b5a..f0d9ccce852814c9fe7314361b4b12cbcbceec9e 100644
--- a/third_party/WebKit/Source/platform/text/TextEncodingDetector.cpp
+++ b/third_party/WebKit/Source/platform/text/TextEncodingDetector.cpp
@@ -52,7 +52,14 @@ bool detectTextEncoding(const char* data,
       CompactEncDet::WEB_CORPUS,
       false,  // Include 7-bit encodings to detect ISO-2022-JP
       &consumedBytes, &isReliable);
-  if (encoding == UNKNOWN_ENCODING)
+
+  // Should return false if the detected encoding is UTF8. This helps prevent
+  // modern web sites from neglecting proper encoding labelling and simply
+  // relying on browser-side encoding detection. Encoding detection is supposed
+  // to work for web sites with legacy encoding only. Detection failure leads
+  // |TextResourceDecoder| to use its default encoding determined from system
+  // locale or TLD.
+  if (encoding == UNKNOWN_ENCODING || encoding == UTF8)
     return false;
 
   // 7-bit encodings (except ISO-2022-JP) are not supported in WHATWG encoding