Use command line to signal whether a child process was passed V8 snapshot files via file descriptor

ash/shell/content_client/shell_content_browser_client.h

Index: ash/shell/content_client/shell_content_browser_client.h
diff --git a/ash/shell/content_client/shell_content_browser_client.h b/ash/shell/content_client/shell_content_browser_client.h
index df62338d8e4cc013fc01d76b501d884e1e69154b..9ee3373f907959048a81e2645535dd70abb25d49 100644
--- a/ash/shell/content_client/shell_content_browser_client.h
+++ b/ash/shell/content_client/shell_content_browser_client.h
@@ -33,6 +33,8 @@ class ShellContentBrowserClient : public content::ContentBrowserClient {
       content::BrowserContext* browser_context,
       content::ProtocolHandlerMap* protocol_handlers,
       content::URLRequestInterceptorScopedVector request_interceptors) override;
+  void AppendExtraCommandLineSwitches(base::CommandLine* command_line,
+                                      int child_process_id) override;
 #if defined(OS_POSIX) && !defined(OS_MACOSX)
   void GetAdditionalMappedFilesForChildProcess(
       const base::CommandLine& command_line,