Expand clickable area of combobutton's dropdown indicator.

BUG=363540
TEST=manually tested.

Review URL: https://codereview.chromium.org/255823002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@266515 0039d316-1c4b-4281-b951-d872f2087c98

ui/file_manager/file_manager/foreground/css/combobutton.css

@@ -21,6 +21,16 @@
   width: 22px;
 }
 
+/* This pseudo element expands clickable area of the .trigger */
+.buttonbar .combobutton > .trigger::before {
+  content: '';
+  display: block;
+  height: 31px;
+  position: absolute;
+  top: -5px;
+  width: 30px;
+}
+
 .buttonbar .combobutton:not([multiple]) > .trigger {
   display: none;
 }