Fix assertion failure in range.mm while examining system dictionary popup.

chrome/browser/renderer_host/text_input_client_message_filter.mm

Index: chrome/browser/renderer_host/text_input_client_message_filter.mm
diff --git a/chrome/browser/renderer_host/text_input_client_message_filter.mm b/chrome/browser/renderer_host/text_input_client_message_filter.mm
index 7bfbdfc2f31675fed554254a8cbdd74c456ee0aa..f86766615896526d90edbbcd431e08d5527a0a62 100644
--- a/chrome/browser/renderer_host/text_input_client_message_filter.mm
+++ b/chrome/browser/renderer_host/text_input_client_message_filter.mm
@@ -43,6 +43,11 @@ bool TextInputClientMessageFilter::OnMessageReceived(
 
 void TextInputClientMessageFilter::OnGotCharacterIndexForPoint(size_t index) {
   TextInputClientMac* service = TextInputClientMac::GetInstance();
+  // |index| could be WTF::notFound (-1) and it's value is different from
+  // NSNotFound so we need to convert it.
+  if (index == static_cast<size_t>(-1)) {
+    index = NSNotFound;
+  }
   service->SetCharacterIndexAndSignal(index);
 }