ui/aura: list aura_export.h in the sources list of aura target

Header files should be listed in the sources list, so gn analyze
can work.

https://docs.google.com/spreadsheets/d/15az3FMl-jAS0mx4E9XVSBVHVpmEzo-9EAGY0ywe7bZs/edit#gid=0

https://groups.google.com/a/chromium.org/d/topic/chromium-dev/1kK45mVemBc/discussion

BUG=661774
TBR=jamescook@chromium.org

Change-Id: I68020668044858be898ce6d18392ee8610cf22f4
Reviewed-on: https://chromium-review.googlesource.com/531030
Commit-Queue: Thiago Farina <tfarina@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#478819}

ash/shell/panel_window.h

@@ -6,7 +6,6 @@
 #define ASH_SHELL_PANEL_WINDOW_H_
 
 #include "base/macros.h"
-#include "ui/aura/aura_export.h"
 #include "ui/views/widget/widget.h"
 #include "ui/views/widget/widget_delegate.h"
 

build/check_gn_headers_whitelist.txt

@@ -375,7 +375,6 @@ ui/accessibility/ax_export.h
 ui/app_list/app_list_export.h
 ui/app_list/app_list_item.h
 ui/app_list/app_list_switches.h
-ui/aura/aura_export.h
 ui/base/clipboard/clipboard_test_template.h
 ui/base/dragdrop/download_file_interface.h
 ui/compositor/compositor_constants.h

ui/aura/BUILD.gn

@@ -77,6 +77,7 @@ component("aura") {
     "window_tree_host_platform.h",
   ]
   sources = [
+    "aura_export.h",
     "client/aura_constants.cc",
     "client/capture_client.cc",
     "client/cursor_client.cc",

ui/aura/test/test_window_parenting_client.h

@@ -7,7 +7,6 @@
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
-#include "ui/aura/aura_export.h"
 #include "ui/aura/client/window_parenting_client.h"
 
 namespace aura {