[File Manager] Support HiDPI images in action picker and default action picker

chrome/browser/resources/file_manager/css/combobutton.css

Index: chrome/browser/resources/file_manager/css/combobutton.css
diff --git a/chrome/browser/resources/file_manager/css/combobutton.css b/chrome/browser/resources/file_manager/css/combobutton.css
index a4689f76b9aa5604db58509dfa97b2b17cec7d43..e21e1c0624bac0d3faf8bdfd9c6e293d8753aaac 100644
--- a/chrome/browser/resources/file_manager/css/combobutton.css
+++ b/chrome/browser/resources/file_manager/css/combobutton.css
@@ -7,30 +7,22 @@
   display: -webkit-box;
 }
 
-.buttonbar .combobutton > img {
-  display: block;
-  height: 16px;
-  margin-bottom: 6px;
-  margin-right: 4px;
-  margin-top: 6px;
-  width: 16px;
+.buttonbar .combobutton > .action {
+  background-position: left center;
+  background-repeat: no-repeat;
+  background-size: 16px 16px;
+  padding-left: 21px;
 }
 
-.buttonbar .combobutton > span {
-  -webkit-box-flex: 1;
-  display: block;
-}
-
-.buttonbar .combobutton > div {
+.buttonbar .combobutton > .trigger {
   border-left: solid 1px #dcdcdc;
-  display: none;
   margin-left: 8px;
   margin-right: -8px;
   width: 22px;
 }
 
-.buttonbar .combobutton[multiple] > div {
-  display: block;
+.buttonbar .combobutton:not([multiple]) > .trigger {
+  display: none;
 }
 
 .buttonbar .combobutton > div > span.disclosureindicator {