Fix header includes for brillo/supprocess

Chrome OS moved these files into a new directory a while
ago. Unfortunately in the last CrOS to AOSP merge, these were reverted
instead of being guarded by __CHROMEOS__. This CL does that.

Bug: 163153182
Test: FEATURES=test emerge-reef update_engine

Change-Id: If56cf95b9cecbb2f9dee74e41636bd90f9ace60b
diff --git a/common/http_fetcher_unittest.cc b/common/http_fetcher_unittest.cc
index 589579e..9338087 100644
--- a/common/http_fetcher_unittest.cc
+++ b/common/http_fetcher_unittest.cc
@@ -37,7 +37,11 @@
 #include <brillo/message_loops/base_message_loop.h>
 #include <brillo/message_loops/message_loop.h>
 #include <brillo/message_loops/message_loop_utils.h>
+#ifdef __CHROMEOS__
+#include <brillo/process/process.h>
+#else
 #include <brillo/process.h>
+#endif  // __CHROMEOS__
 #include <brillo/streams/file_stream.h>
 #include <brillo/streams/stream.h>
 #include <gtest/gtest.h>