Update WebUI for HiDPI images added in r143476

chrome/browser/resources/plugins.css

Index: chrome/browser/resources/plugins.css
diff --git a/chrome/browser/resources/plugins.css b/chrome/browser/resources/plugins.css
index a585fc2bc185b5ecc23d97f9f3673f763a7f8e43..b11dffde66daeb5f0559395df911c74832551606 100644
--- a/chrome/browser/resources/plugins.css
+++ b/chrome/browser/resources/plugins.css
@@ -25,7 +25,10 @@ div#header {
 }
 
 #header h1 {
-  background: url('../../app/theme/default_100_percent/extensions_section.png') 0 20px no-repeat;
+  background: -webkit-image-set(
+      url('../../app/theme/default_100_percent/extensions_section.png') 1x,
+      url('../../app/theme/default_200_percent/extensions_section.png') 2x)
+      0 20px no-repeat;
   display: inline;
   margin: 0;
   padding-bottom: 20px;
@@ -34,7 +37,10 @@ div#header {
 }
 
 html[dir=rtl] #header h1 {
-  background: url('../../app/theme/default_100_percent/extensions_section.png') right no-repeat;
+  background: -webkit-image-set(
+      url('../../app/theme/default_100_percent/extensions_section.png') 1x,
+      url('../../app/theme/default_200_percent/extensions_section.png') 2x)
+      right no-repeat;
   padding-left: 0;
   padding-right: 95px;
 }