Revert of Replace ICU with CED for auto encoding detection

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 abda74b2b62b0e43cb7d1f4395e99bd359ce5ec6..616aac0114d74ae3f284b97a740124242c7c7e3e 100644
--- a/third_party/WebKit/Source/platform/text/TextEncodingDetector.cpp
+++ b/third_party/WebKit/Source/platform/text/TextEncodingDetector.cpp
@@ -30,8 +30,9 @@
 
 #include "platform/text/TextEncodingDetector.h"
 
-#include "third_party/ced/src/compact_enc_det/compact_enc_det.h"
 #include "wtf/text/TextEncoding.h"
+#include <unicode/ucnv.h>
+#include <unicode/ucsdet.h>
 
 namespace blink {
 
@@ -39,20 +40,75 @@
     const char* hintEncodingName, WTF::TextEncoding* detectedEncoding)
 {
     *detectedEncoding = WTF::TextEncoding();
-    int consumedBytes;
-    bool isReliable;
-    Encoding encoding = CompactEncDet::DetectEncoding(
-        data, length, nullptr, nullptr, nullptr,
-        EncodingNameAliasToEncoding(hintEncodingName),
-        UNKNOWN_LANGUAGE,
-        CompactEncDet::WEB_CORPUS,
-        false, // Include 7-bit encodings
-        &consumedBytes,
-        &isReliable);
-    if (encoding != UNKNOWN_ENCODING) {
-        *detectedEncoding = WTF::TextEncoding(MimeEncodingName(encoding));
+    int matchesCount = 0;
+    UErrorCode status = U_ZERO_ERROR;
+    UCharsetDetector* detector = ucsdet_open(&status);
+    if (U_FAILURE(status))
+        return false;
+    ucsdet_enableInputFilter(detector, true);
+    ucsdet_setText(detector, data, static_cast<int32_t>(length), &status);
+    if (U_FAILURE(status))
+        return false;
+
+    // FIXME: A few things we can do other than improving
+    // the ICU detector itself.
+    // 1. Use ucsdet_detectAll and pick the most likely one given
+    // "the context" (parent-encoding, referrer encoding, etc).
+    // 2. 'Emulate' Firefox/IE's non-Universal detectors (e.g.
+    // Chinese, Japanese, Russian, Korean and Hebrew) by picking the
+    // encoding with a highest confidence among the detector-specific
+    // limited set of candidate encodings.
+    // Below is a partial implementation of the first part of what's outlined
+    // above.
+    const UCharsetMatch** matches = ucsdet_detectAll(detector, &matchesCount, &status);
+    if (U_FAILURE(status)) {
+        ucsdet_close(detector);
+        return false;
+    }
+
+    const char* encoding = 0;
+    if (hintEncodingName) {
+        WTF::TextEncoding hintEncoding(hintEncodingName);
+        // 10 is the minimum confidence value consistent with the codepoint
+        // allocation in a given encoding. The size of a chunk passed to
+        // us varies even for the same html file (apparently depending on
+        // the network load). When we're given a rather short chunk, we
+        // don't have a sufficiently reliable signal other than the fact that
+        // the chunk is consistent with a set of encodings. So, instead of
+        // setting an arbitrary threshold, we have to scan all the encodings
+        // consistent with the data.
+        const int32_t kThresold = 10;
+        for (int i = 0; i < matchesCount; ++i) {
+            int32_t confidence = ucsdet_getConfidence(matches[i], &status);
+            if (U_FAILURE(status)) {
+                status = U_ZERO_ERROR;
+                continue;
+            }
+            if (confidence < kThresold)
+                break;
+            const char* matchEncoding = ucsdet_getName(matches[i], &status);
+            if (U_FAILURE(status)) {
+                status = U_ZERO_ERROR;
+                continue;
+            }
+            if (WTF::TextEncoding(matchEncoding) == hintEncoding) {
+                encoding = hintEncodingName;
+                break;
+            }
+        }
+    }
+    // If no match is found so far, just pick the top match.
+    // This can happen, say, when a parent frame in EUC-JP refers to
+    // a child frame in Shift_JIS and both frames do NOT specify the encoding
+    // making us resort to auto-detection (when it IS turned on).
+    if (!encoding && matchesCount > 0)
+        encoding = ucsdet_getName(matches[0], &status);
+    if (U_SUCCESS(status)) {
+        *detectedEncoding = WTF::TextEncoding(encoding);
+        ucsdet_close(detector);
         return true;
     }
+    ucsdet_close(detector);
     return false;
 }