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/extent_writer.h b/extent_writer.h
index db24b4b..883507a 100644
--- a/extent_writer.h
+++ b/extent_writer.h
@@ -6,7 +6,9 @@
 #define UPDATE_ENGINE_EXTENT_WRITER_H_
 
 #include <vector>
-#include "base/logging.h"
+
+#include <base/logging.h>
+
 #include "update_engine/update_metadata.pb.h"
 #include "update_engine/utils.h"