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

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

Index: third_party/WebKit/Source/core/editing/InputMethodController.cpp
diff --git a/third_party/WebKit/Source/core/editing/InputMethodController.cpp b/third_party/WebKit/Source/core/editing/InputMethodController.cpp
index eedf26046cc6765274d95f26be938f1ba1cd3882..a663c1eec032326508173a6bb2be2ce1f3cd6efe 100644
--- a/third_party/WebKit/Source/core/editing/InputMethodController.cpp
+++ b/third_party/WebKit/Source/core/editing/InputMethodController.cpp
@@ -352,15 +352,14 @@ static int computeAbsoluteCaretPosition(size_t textStart,
 
 void InputMethodController::addCompositionUnderlines(
     const Vector<CompositionUnderline>& underlines,
-    ContainerNode* rootEditableElement,
-    unsigned offset) {
+    ContainerNode* baseElement,
+    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;
 
@@ -608,7 +607,10 @@ void InputMethodController::setComposition(
     return;
   }
 
-  addCompositionUnderlines(underlines, baseNode->parentNode(), baseOffset);
+  PlainTextRange compositionPlainTextRange =
+      PlainTextRange::create(*baseNode->parentNode(), *m_compositionRange);
+  addCompositionUnderlines(underlines, baseNode->parentNode(),

[rlanday, 2017/02/16 00:37:54]

Unfortunately I can't just work with baseNode directly here because it's not
necessarily a ContainerNode, so I'm using the parent instead and getting the
composition's plain text offset to the parent.

+                           compositionPlainTextRange.start());
 }
 
 PlainTextRange InputMethodController::createSelectionRangeForSetComposition(