Move --user-agent overriding logic from chrome into content.

content/app/content_main_runner.cc

Index: content/app/content_main_runner.cc
diff --git a/content/app/content_main_runner.cc b/content/app/content_main_runner.cc
index 8d360c37ed1a76610e6a72a1f03cae845b914760..3d363dccc4c8ceb3dc2fbff2003957f3fe86c09a 100644
--- a/content/app/content_main_runner.cc
+++ b/content/app/content_main_runner.cc
@@ -223,9 +223,10 @@ int RunZygote(const content::MainFunctionParams& main_function_params,
   // If a custom user agent was passed on the command line, we need
   // to (re)set it now, rather than using the default one the zygote
   // initialized.
-  bool custom = false;
-  std::string ua = content::GetContentClient()->GetUserAgent(&custom);
-  if (custom) webkit_glue::SetUserAgent(ua, custom);
+  if (command_line.HasSwitch(switches::kUserAgent)) {
+    webkit_glue::SetUserAgent(
+        command_line.GetSwitchValueASCII(switches::kUserAgent), true);
+  }
 
   // The StatsTable must be initialized in each process; we already
   // initialized for the browser process, now we need to initialize
@@ -467,6 +468,16 @@ class ContentMainRunnerImpl : public content::ContentMainRunner {
     if (delegate)
       delegate->PreSandboxStartup();
 
+    // Set any custom user agent passed on the command line now so the string
+    // doesn't change between calls to webkit_glue::GetUserAgent(), otherwise it
+    // defaults to the user agent set during SetContentClient().
+    DCHECK(content::GetContentClient())
+        << "SetContentClient() must be called by this point in time";

[jam, 2012/04/06 23:13:52]

nit: are you sure this dcheck is necessary? ie. have you tried not setting it
and seen that you can get this far without a crash somewhere?

[scherkus (not reviewing), 2012/04/06 23:59:41]

if the call to SetContentClient() happens after setting a custom UA the it would
get clobbered due to SetContentClient() setting the default UA string

so really the DCHECK() is for protecting --user-agent but I suppose it could get
moved later down

I'll give it a shot

[jam, 2012/04/07 00:03:07]

just to be clear, i meant if there's code in content that's called earlier than
this point which does "content::GetContentClient()->". so it'd crash which is as
good a signal as this dcheck

+    if (command_line.HasSwitch(switches::kUserAgent)) {
+      webkit_glue::SetUserAgent(
+          command_line.GetSwitchValueASCII(switches::kUserAgent), true);
+    }
+
     if (!process_type.empty())
       CommonSubprocessInit(process_type);