Suppress text dump of JavaScript modal dialog messages in testharness.js tests

components/test_runner/test_runner.h

Index: components/test_runner/test_runner.h
diff --git a/components/test_runner/test_runner.h b/components/test_runner/test_runner.h
index 532868beb80c2fc15049ee97bb544004f9ce9147..5f93c52fb356ef0063d0ceff6d96c96a3ba03e54 100644
--- a/components/test_runner/test_runner.h
+++ b/components/test_runner/test_runner.h
@@ -173,6 +173,7 @@ class TestRunner : public WebTestRunner {
   void DidCloseChooser();
 
   bool ShouldDumpConsoleMessages() const;
+  bool ShouldDumpJavaScriptDialogs() const;
 
   blink::WebEffectiveConnectionType effective_connection_type() const {
     return effective_connection_type_;
@@ -472,6 +473,10 @@ class TestRunner : public WebTestRunner {
   // to test output.
   void SetDumpConsoleMessages(bool value);
 
+  // Controls whether JavaScript dialogs such as alert() are dumped to test
+  // output.
+  void SetDumpJavaScriptDialogs(bool value);
+
   // Overrides the NetworkQualityEstimator's estimated network type. If |type|
   // is TypeUnknown the NQE's value is used. Be sure to call this with
   // TypeUnknown at the end of your test if you use this.