Revert of Move content's shell connections to the IO thread

content/browser/browser_context.cc

Index: content/browser/browser_context.cc
diff --git a/content/browser/browser_context.cc b/content/browser/browser_context.cc
index 4b0f2b161f55ce1d5db9875ee0c9cd9846ac01f8..4ce64856c56e33762382905f30fdc56cdd0ef171 100644
--- a/content/browser/browser_context.cc
+++ b/content/browser/browser_context.cc
@@ -152,9 +152,7 @@
       std::unique_ptr<shell::Connection> connection,
       shell::mojom::ServiceRequest request)
       : root_connection_(std::move(connection)),
-        shell_connection_(MojoShellConnection::Create(
-            std::move(request),
-            BrowserThread::GetMessageLoopProxyForThread(BrowserThread::IO))) {}
+        shell_connection_(MojoShellConnection::Create(std::move(request))) {}
   ~BrowserContextShellConnectionHolder() override {}
 
   MojoShellConnection* shell_connection() { return shell_connection_.get(); }
@@ -435,7 +433,6 @@
     browser_context->SetUserData(kMojoShellConnection, connection_holder);
 
     MojoShellConnection* connection = connection_holder->shell_connection();
-    connection->Start();
 
     // New embedded service factories should be added to |connection| here.