Export URLRequestContextBuilder::SchemeFactory

The inner class needs to be exported in case any uses in inline methods
or vtable of the outer class causes it to potentially be referenced across
a shared library boundary.

On non-Windows, the visibility attribute is already inherited by nested
classes, but on Windows, they must be marked explicitly.

BUG=82385

Review URL: https://codereview.chromium.org/464563004

Cr-Commit-Position: refs/heads/master@{#289093}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289093 0039d316-1c4b-4281-b951-d872f2087c98

net/url_request/url_request_context_builder.h

@@ -168,7 +168,7 @@ class NET_EXPORT URLRequestContextBuilder {
   URLRequestContext* Build();
 
  private:
-  struct SchemeFactory {
+  struct NET_EXPORT SchemeFactory {
     SchemeFactory(const std::string& scheme,
                   net::HttpAuthHandlerFactory* factory);
     ~SchemeFactory();