Add DCHECK to detect when a RPH is reused with a different context.

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 1792b84b62471e9e96e76012ef7177f2e2982c8e..a98777ece0a495dfc469a0385aa6374ec0fdc82a 100644
--- a/content/browser/renderer_host/render_process_host_impl.cc
+++ b/content/browser/renderer_host/render_process_host_impl.cc
@@ -2131,8 +2131,11 @@ void RenderProcessHostImpl::FilterURL(RenderProcessHost* rph,
 bool RenderProcessHostImpl::IsSuitableHost(RenderProcessHost* host,
                                            BrowserContext* browser_context,
                                            const GURL& site_url) {
-  if (run_renderer_in_process())
+  if (run_renderer_in_process()) {
+    DCHECK_EQ(host->GetBrowserContext(), browser_context)
+        << " Single-process mode does not support multiple browser contexts.";
     return true;
+  }
 
   if (host->GetBrowserContext() != browser_context)
     return false;