Include the implemented header first in all projects.

The Google C++ style guide dictates that foo.cc and foo_unittest.cc
should include foo.h in the first place, so missing headers in foo.h
are detected with a compile error of the module implementing them and
not when another module uses them.

This CL sweeps across all the .cc file in platform2 enforcing this.

BUG=None
TEST=cbuildbot amd64-generic

Change-Id: I41835835caba13f54c3c844ecf552eb0e47efa9d
Reviewed-on: https://chromium-review.googlesource.com/228894
Tested-by: Alex Deymo <deymo@chromium.org>
Reviewed-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/download_action.cc b/download_action.cc
index f37828b..35b1174 100644
--- a/download_action.cc
+++ b/download_action.cc
@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "update_engine/download_action.h"
+
 #include <errno.h>
 #include <algorithm>
 #include <string>