Add a flag for headless: --block_new_web_contents.

It's an alternative to specifying the option via the
options builder.

Change-Id: I6a0034048dea433c59f1164beac96d1d3b059d7c
Reviewed-on: https://chromium-review.googlesource.com/1081275
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Johannes Henkel <johannes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#563792}

headless/app/headless_shell.cc

@@ -819,6 +819,9 @@ int HeadlessShellMain(int argc, const char** argv) {
     }
   }
 
+  if (command_line.HasSwitch(switches::kBlockNewWebContents))
+    builder.SetBlockNewWebContents(true);
+
   return HeadlessBrowserMain(
       builder.Build(),
       base::BindOnce(&HeadlessShell::OnStart, base::Unretained(&shell)));

headless/app/headless_shell_switches.cc

@@ -117,5 +117,7 @@ const char kAuthServerWhitelist[] = "auth-server-whitelist";
 // Possible values: none|slight|medium|full|max. Default: full.
 const char kFontRenderHinting[] = "font-render-hinting";
 
+// If true, then all pop-ups and calls to window.open will fail.
+const char kBlockNewWebContents[] = "block-new-web-contents";
 }  // namespace switches
 }  // namespace headless

headless/app/headless_shell_switches.h

@@ -35,6 +35,7 @@ extern const char kVirtualTimeBudget[];
 extern const char kWindowSize[];
 extern const char kAuthServerWhitelist[];
 extern const char kFontRenderHinting[];
+extern const char kBlockNewWebContents[];
 
 // Switches which are replicated from content.
 using ::switches::kRemoteDebuggingPort;