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

components/test_runner/text_input_controller.cc

Index: components/test_runner/text_input_controller.cc
diff --git a/components/test_runner/text_input_controller.cc b/components/test_runner/text_input_controller.cc
index 788570bb87e9b0a8d6abebca3c641b7af5ec59fe..cd0aa73b8f394b3e6d7c1649e954ae49c103fd5f 100644
--- a/components/test_runner/text_input_controller.cc
+++ b/components/test_runner/text_input_controller.cc
@@ -283,14 +283,18 @@ void TextInputController::SetComposition(const std::string& text) {
   key_down.windowsKeyCode = 0xE5;  // VKEY_PROCESSKEY
   view()->handleInputEvent(key_down);
 
+  // The value returned by std::string::length() may not correspond to the
+  // actual number of encoded characters in sequences of multi-byte or
+  // variable-length characters.
+  blink::WebString newText = blink::WebString::fromUTF8(text);
+  size_t textLength = newText.length();
+
   std::vector<blink::WebCompositionUnderline> underlines;
-  underlines.push_back(blink::WebCompositionUnderline(0, text.length(),
-                                                      SK_ColorBLACK, false,
-                                                      SK_ColorTRANSPARENT));
+  underlines.push_back(blink::WebCompositionUnderline(
+      0, textLength, SK_ColorBLACK, false, SK_ColorTRANSPARENT));
   view()->setComposition(
-      blink::WebString::fromUTF8(text),
-      blink::WebVector<blink::WebCompositionUnderline>(underlines),
-      text.length(), text.length());
+      newText, blink::WebVector<blink::WebCompositionUnderline>(underlines),
+      textLength, textLength);
 }
 
 blink::WebView* TextInputController::view() {