update_engine: fixed warnings from cpplint

Fixed all the cpplint warnings in update engine.

BUG=None
TEST=Unit tests still pass.

Change-Id: I285ae858eec8abe0b26ff203b99a42a200ceb71c
Reviewed-on: https://chromium-review.googlesource.com/204027
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/constants.h b/constants.h
index 3a74156..826c5ff 100644
--- a/constants.h
+++ b/constants.h
@@ -78,9 +78,9 @@
 // interest to us when looking at UMA metrics) using which we may download
 // the payload.
 typedef enum {
-  kDownloadSourceHttpsServer, // UMA Binary representation: 0001
-  kDownloadSourceHttpServer,  // UMA Binary representation: 0010
-  kDownloadSourceHttpPeer,    // UMA Binary representation: 0100
+  kDownloadSourceHttpsServer,  // UMA Binary representation: 0001
+  kDownloadSourceHttpServer,   // UMA Binary representation: 0010
+  kDownloadSourceHttpPeer,     // UMA Binary representation: 0100
 
   // Note: Add new sources only above this line.
   kNumDownloadSources