More common to include headers than cc files so lets do that

An accidental inclusion of a cc file caused interesting
linking errors (duplicate chrome::kChromeUIPrintURL) in certain
build configurations.

Fix is to include the header instead of the cc file so that
references to chrome::kChromeUIPrintURL will be external as intended.

Change-Id: Iba69dbd17267955534609d308cef16ab0467671d
Reviewed-on: https://chromium-review.googlesource.com/1005342Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#549560}

chrome/browser/printing/print_browsertest.cc

@@ -17,7 +17,7 @@
 #include "chrome/browser/ui/webui/print_preview/print_preview_ui.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/pref_names.h"
-#include "chrome/common/webui_url_constants.cc"
+#include "chrome/common/webui_url_constants.h"
 #include "chrome/test/base/in_process_browser_test.h"
 #include "chrome/test/base/ui_test_utils.h"
 #include "components/prefs/pref_service.h"