Make sure multi chracter codepoints are deleted correctly

content/public/android/java/src/org/chromium/content/browser/input/AdapterInputConnection.java

Index: content/public/android/java/src/org/chromium/content/browser/input/AdapterInputConnection.java
diff --git a/content/public/android/java/src/org/chromium/content/browser/input/AdapterInputConnection.java b/content/public/android/java/src/org/chromium/content/browser/input/AdapterInputConnection.java
index 2e088a354059e624770c343e77546e5bb111711a..9adf69292ab3f7c588a6681aeb1431e7ece67b0d 100644
--- a/content/public/android/java/src/org/chromium/content/browser/input/AdapterInputConnection.java
+++ b/content/public/android/java/src/org/chromium/content/browser/input/AdapterInputConnection.java
@@ -9,7 +9,6 @@ import android.text.Editable;
 import android.text.InputType;
 import android.text.Selection;
 import android.text.TextUtils;
-import android.util.Log;
 import android.view.KeyCharacterMap;
 import android.view.KeyEvent;
 import android.view.View;
@@ -18,6 +17,7 @@ import android.view.inputmethod.EditorInfo;
 import android.view.inputmethod.ExtractedText;
 import android.view.inputmethod.ExtractedTextRequest;
 
+import org.chromium.base.Log;
 import org.chromium.base.VisibleForTesting;
 import org.chromium.blink_public.web.WebInputEventType;
 import org.chromium.blink_public.web.WebTextInputFlags;
@@ -229,8 +229,8 @@ public class AdapterInputConnection extends BaseInputConnection {
         }
         // updateSelection should be called every time the selection or composition changes
         // if it happens not within a batch edit, or at the end of each top level batch edit.
-        getInputMethodManagerWrapper().updateSelection(mInternalView,
-                selectionStart, selectionEnd, compositionStart, compositionEnd);
+        getInputMethodManagerWrapper().updateSelection(
+                mInternalView, selectionStart, selectionEnd, compositionStart, compositionEnd);
         mLastUpdateSelectionStart = selectionStart;
         mLastUpdateSelectionEnd = selectionEnd;
         mLastUpdateCompositionStart = compositionStart;
@@ -350,10 +350,23 @@ public class AdapterInputConnection extends BaseInputConnection {
         return deleteSurroundingTextImpl(beforeLength, afterLength, false);
     }
 
+    /**
+     * Check if the given {@code index} is between UTF-16 surrogate pair.
+     * @param str The String.
+     * @param index The index
+     * @return True if the index is between UTF-16 surrogate pair, false otherwise.
+     */
+    @VisibleForTesting
+    static boolean isIndexBetweenUtf16SurrogatePair(CharSequence str, int index) {
+        return index > 0 && index < str.length() && Character.isHighSurrogate(str.charAt(index - 1))
+                && Character.isLowSurrogate(str.charAt(index));
+    }
+
     private boolean deleteSurroundingTextImpl(
             int beforeLength, int afterLength, boolean fromPhysicalKey) {
         if (DEBUG) {
-            Log.w(TAG, "deleteSurroundingText [" + beforeLength + " " + afterLength + "]");
+            Log.w(TAG, "deleteSurroundingText [" + beforeLength + " " + afterLength + " "
+                            + fromPhysicalKey + "]");
         }
 
         if (mPendingAccent != 0) {
@@ -362,10 +375,22 @@ public class AdapterInputConnection extends BaseInputConnection {
 
         int originalBeforeLength = beforeLength;
         int originalAfterLength = afterLength;
-        int availableBefore = Selection.getSelectionStart(mEditable);
-        int availableAfter = mEditable.length() - Selection.getSelectionEnd(mEditable);
+        int selectionStart = Selection.getSelectionStart(mEditable);
+        int selectionEnd = Selection.getSelectionEnd(mEditable);
+        int availableBefore = selectionStart;
+        int availableAfter = mEditable.length() - selectionEnd;
         beforeLength = Math.min(beforeLength, availableBefore);
         afterLength = Math.min(afterLength, availableAfter);
+
+        // Adjust these values even before calling super.deleteSurroundingText() to be consistent
+        // with the super class.
+        if (isIndexBetweenUtf16SurrogatePair(mEditable, selectionStart - beforeLength)) {
+            beforeLength += 1;
+        }
+        if (isIndexBetweenUtf16SurrogatePair(mEditable, selectionEnd + afterLength)) {
+            afterLength += 1;
+        }
+
         super.deleteSurroundingText(beforeLength, afterLength);
         updateSelectionIfRequired();