Add changes required to build with Clang

Explicitly qualify identifier to find declaration in dependent base class
Make types more consistent (class/struct was used interchangably)
This removes the requirement to specify -Wno-mismatched-tags for Clang

BUG=chromium-os:28749, chromium-os:30434
TEST=Run USE="clang" FEATURES="test" emerge-amd64-generic -v shill

Change-Id: I4a9839b9377d9ac320ab024a57f94603365e1713
CQ-DEPEND=Idac49b9de009c676ac8a2820fc2ce780195d94a4
Reviewed-on: https://gerrit.chromium.org/gerrit/29082
Reviewed-by: Liam McLoughlin <lmcloughlin@chromium.org>
Tested-by: Liam McLoughlin <lmcloughlin@chromium.org>
Commit-Queue: Liam McLoughlin <lmcloughlin@chromium.org>
diff --git a/http_request.h b/http_request.h
index 9108ea5..c554389 100644
--- a/http_request.h
+++ b/http_request.h
@@ -25,7 +25,7 @@
 class Error;
 class EventDispatcher;
 class HTTPURL;
-class InputData;
+struct InputData;
 class IOHandler;
 class IPAddress;
 class Sockets;