Forward-declare AutocompleteMatch as a struct in autocomplete_popup_view_gtk.h

AutocompleteMatch is a struct, and should thus be forward-declared as such.
Otherwise, Clang warns about the mismatch, and we treat the warning as an error.

BUG=49304
TEST=None

Review URL: http://codereview.chromium.org/2805086

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@54777 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/browser/autocomplete/autocomplete_popup_view_gtk.h b/chrome/browser/autocomplete/autocomplete_popup_view_gtk.h
index 0ac3113..61b9f5b 100644
--- a/chrome/browser/autocomplete/autocomplete_popup_view_gtk.h
+++ b/chrome/browser/autocomplete/autocomplete_popup_view_gtk.h
@@ -18,7 +18,7 @@
 
 class AutocompleteEditModel;
 class AutocompleteEditView;
-class AutocompleteMatch;
+struct AutocompleteMatch;
 class AutocompletePopupModel;
 class GtkThemeProvider;
 class Profile;