Flush socket pools and SPDY session pool properly on explicit requests and network changes.

net/base/mock_host_resolver.cc

Index: net/base/mock_host_resolver.cc
diff --git a/net/base/mock_host_resolver.cc b/net/base/mock_host_resolver.cc
index 7f2512f7886f02aa78aafffc6df6278b2129bf48..c079fc1ebe4041d82a2f897638b6162ca5480760 100644
--- a/net/base/mock_host_resolver.cc
+++ b/net/base/mock_host_resolver.cc
@@ -66,6 +66,10 @@ void MockHostResolverBase::RemoveObserver(Observer* observer) {
   impl_->RemoveObserver(observer);
 }
 
+void MockHostResolverBase::Flush() {
+  impl_->Flush();
+}
+
 void MockHostResolverBase::Reset(HostResolverProc* interceptor) {
   synchronous_mode_ = false;