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 729df89e82c5aea8770db483dfdfbb6bdf806e55..3a8d0a4b99fa202ee540c392321326ecab2343b6 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::GetTaskRunnerForThread(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.