Reland: Fix setComposingText with empty text when newCursorPosition != 1

content/renderer/render_widget.cc

Index: content/renderer/render_widget.cc
diff --git a/content/renderer/render_widget.cc b/content/renderer/render_widget.cc
index ee171f595d950efcb2d85b3a3de5361b38a6517a..187edac700de34a8a7379c5d3125d7a8e429f802 100644
--- a/content/renderer/render_widget.cc
+++ b/content/renderer/render_widget.cc
@@ -1508,6 +1508,32 @@ WebRect RenderWidget::windowResizerRect() {
   return resizer_rect_;
 }
 
+std::pair<int, int> RenderWidget::adjustSelectionForBoundary(
+    int selectionStart,
+    int selectionEnd,
+    const int textLength) const {
+  int compositionLength =
+      text_input_info_.compositionEnd - text_input_info_.compositionStart;
+  int beforeCompositionLength;
+  if (compositionLength != 0)
+    beforeCompositionLength = text_input_info_.compositionStart;
+  else
+    beforeCompositionLength = text_input_info_.selectionStart;
+  int afterCompositionLength =
+      static_cast<int>(text_input_info_.value.length()) - compositionLength -
+      beforeCompositionLength;
+
+  // In case of exceeding the left boundary.
+  selectionStart = std::max(selectionStart, -beforeCompositionLength);
+  selectionEnd = std::max(selectionEnd, selectionStart);
+
+  // In case of exceeding the right boundary.
+  selectionEnd = std::min(selectionEnd, textLength + afterCompositionLength);
+  selectionStart = std::min(selectionStart, selectionEnd);
+
+  return std::make_pair(selectionStart, selectionEnd);
+}
+
 void RenderWidget::OnImeSetComposition(
     const base::string16& text,
     const std::vector<WebCompositionUnderline>& underlines,
@@ -1516,9 +1542,13 @@ void RenderWidget::OnImeSetComposition(
   if (!ShouldHandleImeEvent())
     return;
   ImeEventGuard guard(this);
+
+  std::pair<int, int> selectionPair =
+      adjustSelectionForBoundary(selection_start, selection_end, text.length());
+
   if (!webwidget_->setComposition(
       text, WebVector<WebCompositionUnderline>(underlines),
-      selection_start, selection_end)) {
+      selectionPair.first, selectionPair.second)) {
     // If we failed to set the composition text, then we need to let the browser
     // process to cancel the input method's ongoing composition session, to make
     // sure we are in a consistent state.