Convert ContentMain to take a struct instead of parameters that vary depending on the platform.

content/shell/app/shell_content_main.cc

Index: content/shell/app/shell_content_main.cc
===================================================================
--- content/shell/app/shell_content_main.cc	(revision 255697)
+++ content/shell/app/shell_content_main.cc	(working copy)
@@ -11,6 +11,9 @@
 int ContentMain(int argc,
                 const char** argv) {
   content::ShellMainDelegate delegate;
-  return content::ContentMain(argc, argv, &delegate);
+  content::ContentMainParams params(&delegate);
+  params.argc = argc;
+  params.argv = argv;
+  return content::ContentMain(&params);
 }
 #endif  // OS_MACOSX