Add chrome_split_dll gyp variable, and duplicate chrome_main_dll target (reland)

content/browser/renderer_host/render_process_host_impl.cc

Index: content/browser/renderer_host/render_process_host_impl.cc
diff --git a/content/browser/renderer_host/render_process_host_impl.cc b/content/browser/renderer_host/render_process_host_impl.cc
index 51d9298c01545189a725cd2d29cb2c5da5ea87b5..2e7bba8213b63d973faae74ba03d1c3731754d5a 100644
--- a/content/browser/renderer_host/render_process_host_impl.cc
+++ b/content/browser/renderer_host/render_process_host_impl.cc
@@ -496,6 +496,8 @@ bool RenderProcessHostImpl::Init() {
 
   CreateMessageFilters();
 
+  // Single-process mode not supported in split-dll mode.
+#if !defined(CHROME_SPLIT_DLL)
   if (run_renderer_in_process()) {
     // Crank up a thread and run the initialization there.  With the way that
     // messages flow between the browser and renderer, this thread is required
@@ -517,7 +519,9 @@ bool RenderProcessHostImpl::Init() {
     in_process_renderer_->StartWithOptions(options);
 
     OnProcessLaunched();  // Fake a callback that the process is ready.
-  } else {
+  } else
+#endif  // !CHROME_SPLIT_DLL
+  {
     // Build command line for renderer.  We call AppendRendererCommandLine()
     // first so the process type argument will appear first.
     CommandLine* cmd_line = new CommandLine(renderer_path);