update_engine: Standarize mock/fake filenames.

Mock classes implement mostly MOCK_METHOD* methods used with gmock.
Those classes should be named with the prefix "Mock" in the class
name and "mock_" in the header filename.

Fake classes implement a working version of the interface they provide,
often with extra functionality to change their behavior. Those classes
should be prefixed with "Fake" in the class name and "fake_" in the
file name.

Other minor include order fixes are included in this patch.

BUG=None
TEST=Unittest still pass.

Change-Id: I23de7cb11e25182d5855afacca47d431c97b82bb
Reviewed-on: https://chromium-review.googlesource.com/227779
Reviewed-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
Tested-by: Alex Deymo <deymo@chromium.org>
diff --git a/mock_payload_state.h b/mock_payload_state.h
index 2d40a19..2ac7e97 100644
--- a/mock_payload_state.h
+++ b/mock_payload_state.h
@@ -7,7 +7,8 @@
 
 #include <string>
 
-#include "gmock/gmock.h"
+#include <gmock/gmock.h>
+
 #include "update_engine/omaha_request_action.h"
 #include "update_engine/payload_state_interface.h"