Hide console log messages for imported WPT tests

content/shell/test_runner/web_frame_test_client.cc

Index: content/shell/test_runner/web_frame_test_client.cc
diff --git a/content/shell/test_runner/web_frame_test_client.cc b/content/shell/test_runner/web_frame_test_client.cc
index ac85df245e22584c5628b14d64a80034f98aec02..5f334ddb4467b1c12f20660cdccb5f3e230fc21f 100644
--- a/content/shell/test_runner/web_frame_test_client.cc
+++ b/content/shell/test_runner/web_frame_test_client.cc
@@ -648,10 +648,15 @@ void WebFrameTestClient::didAddMessageToConsole(
     default:
       level = "MESSAGE";
   }
-  delegate_->PrintMessage(std::string("CONSOLE ") + level + ": ");
+  std::string console_message(std::string("CONSOLE ") + level + ": ");
   if (source_line) {
-    delegate_->PrintMessage(base::StringPrintf("line %d: ", source_line));
+    console_message += base::StringPrintf("line %d: ", source_line);
   }
+  // Console messages shouldn't be included in the expected output for
+  // web-platform-tests because they may create non-determinism not
+  // intended by the test author. They are still included in the stderr
+  // output for debug purposes.
+  bool dump_to_stderr = test_runner()->is_web_platform_tests_mode();
   if (!message.text.isEmpty()) {
     std::string new_message;
     new_message = message.text.utf8();
@@ -660,9 +665,15 @@ void WebFrameTestClient::didAddMessageToConsole(
       new_message = new_message.substr(0, file_protocol) +
                     URLSuitableForTestResult(new_message.substr(file_protocol));
     }
-    delegate_->PrintMessage(new_message);
+    console_message += new_message;
+  }
+  console_message += "\n";
+
+  if (dump_to_stderr) {
+    delegate_->PrintMessageToStderr(console_message);
+  } else {
+    delegate_->PrintMessage(console_message);
   }
-  delegate_->PrintMessage(std::string("\n"));
 }
 
 blink::WebNavigationPolicy WebFrameTestClient::decidePolicyForNavigation(