Use our own grapheme boundary handling.

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

 /*
  * Copyright (C) 2004, 2005, 2006, 2007 Apple Inc. All rights reserved.
  *
  * 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 24 matching lines @@
 #include "core/editing/EditingStrategy.h"
 #include "core/editing/Editor.h"
 #include "core/editing/PlainTextRange.h"
 #include "core/editing/PositionIterator.h"
 #include "core/editing/VisiblePosition.h"
 #include "core/editing/VisibleSelection.h"
 #include "core/editing/VisibleUnits.h"
 #include "core/editing/iterators/TextIterator.h"
 #include "core/editing/serializers/HTMLInterchange.h"
 #include "core/editing/state_machines/BackspaceStateMachine.h"
+#include "core/editing/state_machines/BackwardGraphemeBoundaryStateMachine.h"
+#include "core/editing/state_machines/ForwardGraphemeBoundaryStateMachine.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/UseCounter.h"
 #include "core/html/HTMLBRElement.h"
 #include "core/html/HTMLDivElement.h"
 #include "core/html/HTMLLIElement.h"
 #include "core/html/HTMLParagraphElement.h"
 #include "core/html/HTMLSpanElement.h"
 #include "core/html/HTMLTableCellElement.h"
 #include "core/html/HTMLUListElement.h"
 #include "core/layout/LayoutObject.h"
@@ skipping 493 matching lines @@
 int findNextBoundaryOffset(const String& str, int current)
 {
     StateMachine machine;
     TextSegmentationMachineState state = TextSegmentationMachineState::Invalid;
 
     for (int i = current - 1; i >= 0; --i) {
         state = machine.feedPrecedingCodeUnit(str[i]);
         if (state != TextSegmentationMachineState::NeedMoreCodeUnit)
             break;
     }
-    if (state == TextSegmentationMachineState::NeedMoreCodeUnit)
+    if (current == 0 || state == TextSegmentationMachineState::NeedMoreCodeUnit)
         state = machine.tellEndOfPrecedingText();
     if (state == TextSegmentationMachineState::Finished)
         return current + machine.finalizeAndGetBoundaryOffset();
     const int length = str.length();
     DCHECK_EQ(TextSegmentationMachineState::NeedFollowingCodeUnit, state);
     for (int i = current; i < length; ++i) {
         state = machine.feedFollowingCodeUnit(str[i]);
         if (state != TextSegmentationMachineState::NeedMoreCodeUnit)
             break;
     }
     return current + machine.finalizeAndGetBoundaryOffset();
 }
 
 int previousGraphemeBoundaryOf(const Node* node, int current)

[yosin_UTC9, 2016/04/07 01:06:53]

Could you add TODO comment that we need to support grapheme crossing |Node|
boundary.

[Seigo Nonaka, 2016/04/07 03:44:59]

Done.

 {
-    if (!node->isTextNode())
+    DCHECK_GE(current, 0);
+    if (current <= 1 || !node->isTextNode())
         return current - 1;
     const String& text = toText(node)->data();
-    if (text.is8Bit())
-        return current - 1; // TODO(nona): Good to support CR x LF.
-    TextBreakIterator* iterator = cursorMovementIterator(text.characters16(), text.length());
-    if (!iterator)
-        return current - 1;
-    const int result = iterator->preceding(current);
-    return result == TextBreakDone ? current - 1 : result;
+    return findNextBoundaryOffset<BackwardGraphemeBoundaryStateMachine>(
+        text, current);

[yosin_UTC9, 2016/04/07 01:06:53]

nit: Could you make this call in one line to follow other parts?

[Seigo Nonaka, 2016/04/07 03:44:59]

Done.

 }
 
 static int previousBackwardDeletionOffsetOf(const Node* node, int current)
 {
     DCHECK_GE(current, 0);
     if (current <= 1)
         return 0;
     if (!node->isTextNode())
         return current - 1;
 
     const String& text = toText(node)->data();
     DCHECK_LT(static_cast<unsigned>(current - 1), text.length());
     return findNextBoundaryOffset<BackspaceStateMachine>(text, current);
 }
 
 int nextGraphemeBoundaryOf(const Node* node, int current)
 {
     if (!node->isTextNode())

[yosin_UTC9, 2016/04/07 01:06:53]

Could you add TODO comment that we need to support grapheme crossing |Node|
boundary.

[Seigo Nonaka, 2016/04/07 03:44:59]

Done.

         return current + 1;
     const String& text = toText(node)->data();
-    if (text.is8Bit())
-        return current + 1; // TODO(nona): Good to support CR x LF.
-    TextBreakIterator* iterator = cursorMovementIterator(text.characters16(), text.length());
-    if (!iterator)
+    const int length = text.length();
+    DCHECK_LE(current, length);
+    if (current >= (length - 1))

[yosin_UTC9, 2016/04/07 01:06:53]

nit: We don't need to have parenthesis for |(length - 1)|.

[Seigo Nonaka, 2016/04/07 03:44:59]

Done.

         return current + 1;
-    const int result = iterator->following(current);
-    return result == TextBreakDone ? current + 1 : result;
+    return findNextBoundaryOffset<ForwardGraphemeBoundaryStateMachine>(
+        text, current);

[yosin_UTC9, 2016/04/07 01:06:53]

nit: Could you make this call in one line to follow other parts?

[Seigo Nonaka, 2016/04/07 03:44:59]

Done.

 }
 
 template <typename Strategy>
 PositionTemplate<Strategy> previousPositionOfAlgorithm(const PositionTemplate<Strategy>& position, PositionMoveType moveType)
 {
     Node* const node = position.anchorNode();
     if (!node)
         return position;
 
     const int offset = position.computeEditingOffset();
@@ skipping 1082 matching lines @@
     // instead of possibly at the end of the last node before the selection
     return mostForwardCaretPosition(visiblePosition.deepEquivalent());
 }
 
 bool isTextSecurityNode(const Node* node)
 {
     return node && node->layoutObject() && node->layoutObject()->style()->textSecurity() != TSNONE;
 }
 
 } // namespace blink