Fix bug on Android causing composition underlines to appear in the wrong place

third_party/WebKit/Source/core/editing/InputMethodController.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 334 matching lines @@
 
 // relativeCaretPosition is relative to the end of the text.
 static int computeAbsoluteCaretPosition(size_t textStart,
                                         size_t textLength,
                                         int relativeCaretPosition) {
   return textStart + textLength + relativeCaretPosition;
 }
 
 void InputMethodController::addCompositionUnderlines(
     const Vector<CompositionUnderline>& underlines,
-    ContainerNode* rootEditableElement,
-    unsigned offset) {
+    ContainerNode* baseElement,

[yosin_UTC9, 2017/02/20 06:29:10]

Please do renaming in another patch for ease of reviewing.
It is hard to identify which change fix the issue. 

+    unsigned offsetInPlainChars) {
   for (const auto& underline : underlines) {
-    unsigned underlineStart = offset + underline.startOffset();
-    unsigned underlineEnd = offset + underline.endOffset();
+    unsigned underlineStart = offsetInPlainChars + underline.startOffset();
+    unsigned underlineEnd = offsetInPlainChars + underline.endOffset();
 
     EphemeralRange ephemeralLineRange =
-        PlainTextRange(underlineStart, underlineEnd)
-            .createRange(*rootEditableElement);
+        PlainTextRange(underlineStart, underlineEnd).createRange(*baseElement);
     if (ephemeralLineRange.isNull())
       continue;
 
     document().markers().addCompositionMarker(
         ephemeralLineRange.startPosition(), ephemeralLineRange.endPosition(),
         underline.color(), underline.thick(), underline.backgroundColor());
   }
 }
 
 bool InputMethodController::replaceCompositionAndMoveCaret(
@@ skipping 227 matching lines @@
   setEditableSelectionOffsets(selectedRange, NotUserTriggered);
 
   if (underlines.isEmpty()) {
     document().markers().addCompositionMarker(
         m_compositionRange->startPosition(), m_compositionRange->endPosition(),
         Color::black, false,
         LayoutTheme::theme().platformDefaultCompositionBackgroundColor());
     return;
   }
 
-  addCompositionUnderlines(underlines, baseNode->parentNode(), baseOffset);
+  PlainTextRange compositionPlainTextRange =

[yosin_UTC9, 2017/02/20 06:29:10]

nit: s/PlainTextRange/const PlainTextRange/

+      PlainTextRange::create(*baseNode->parentNode(), *m_compositionRange);
+  addCompositionUnderlines(underlines, baseNode->parentNode(),
+                           compositionPlainTextRange.start());
 }
 
 PlainTextRange InputMethodController::createSelectionRangeForSetComposition(
     int selectionStart,
     int selectionEnd,
     size_t textLength) const {
   const int selectionOffsetsStart =
       static_cast<int>(getSelectionOffsets().start());
   const int start = selectionOffsetsStart + selectionStart;
   const int end = selectionOffsetsStart + selectionEnd;
@@ skipping 462 matching lines @@
   frame().chromeClient().resetInputMethod();
 }
 
 DEFINE_TRACE(InputMethodController) {
   visitor->trace(m_frame);
   visitor->trace(m_compositionRange);
   SynchronousMutationObserver::trace(visitor);
 }
 
 }  // namespace blink