Fix cluster-fuzz crash with internal EventSender API.

content/shell/renderer/test_runner/event_sender.cc

Index: content/shell/renderer/test_runner/event_sender.cc
diff --git a/content/shell/renderer/test_runner/event_sender.cc b/content/shell/renderer/test_runner/event_sender.cc
index f1acaadfbb624afcf6913cf6a7488535dfc2b5e0..a6482a7d3c5bd244f76ad30bdee9e107b112904f 100644
--- a/content/shell/renderer/test_runner/event_sender.cc
+++ b/content/shell/renderer/test_runner/event_sender.cc
@@ -1375,7 +1375,12 @@ void EventSender::KeyDown(const std::string& code_str,
     if (!code) {
       WebString web_code_str =
           WebString::fromUTF8(code_str.data(), code_str.size());
-      DCHECK_EQ(1u, web_code_str.length());
+      if (web_code_str.length() != 1u) {
+        v8::Isolate* isolate = blink::mainThreadIsolate();
+        isolate->ThrowException(v8::Exception::TypeError(
+            gin::StringToV8(isolate, "Invalid web code.")));
+        return;
+      }
       text = code = web_code_str.at(0);
       needs_shift_key_modifier = NeedsShiftModifier(code);
       if ((code & 0xFF) >= 'a' && (code & 0xFF) <= 'z')