Revert of HttpCache::Transaction layer allowing parallel validation

net/http/http_transaction_test_util.cc

Index: net/http/http_transaction_test_util.cc
diff --git a/net/http/http_transaction_test_util.cc b/net/http/http_transaction_test_util.cc
index fa42dd78f5a0c19cce3d4a0c0329ce8f08742cb5..a5b57461df5a2e49568fa045bc285f9d01e006bc 100644
--- a/net/http/http_transaction_test_util.cc
+++ b/net/http/http_transaction_test_util.cc
@@ -409,6 +409,13 @@
   if (!t)
     return ERR_FAILED;
 
+  if (!before_network_start_callback_.is_null()) {
+    bool defer = false;
+    before_network_start_callback_.Run(&defer);
+    if (defer)
+      return net::ERR_IO_PENDING;
+  }
+
   test_mode_ = t->test_mode;
 
   // Return immediately if we're returning an error.
@@ -459,16 +466,6 @@
   if (request_->load_flags & LOAD_PREFETCH)
     response_.unused_since_prefetch = true;
 
-  // Pause and resume.
-  if (!before_network_start_callback_.is_null()) {
-    bool defer = false;
-    before_network_start_callback_.Run(&defer);
-    if (defer) {
-      callback_ = callback;
-      return net::ERR_IO_PENDING;
-    }
-  }
-
   if (test_mode_ & TEST_MODE_SYNC_NET_START)
     return OK;
 
@@ -485,9 +482,8 @@
     const BeforeHeadersSentCallback& callback) {}
 
 int MockNetworkTransaction::ResumeNetworkStart() {
-  DCHECK(!callback_.is_null());
-  CallbackLater(callback_, OK);
-  return ERR_IO_PENDING;
+  // Should not get here.
+  return ERR_FAILED;
 }
 
 void MockNetworkTransaction::GetConnectionAttempts(