Compact links: Avoid duplicate call of filterByCommonLanguages

It re-triggers mw.uls.getFrequentLanguageList(),
getPreviousLanguages() and localstorage read.

In this patch the result was saved and reused.

Bug: T122341
Change-Id: I14839eb611cd3e995e8d8ab729ee3f714840f9ad

resources/js/ext.uls.compactlinks.js

@@ -47,6 +47,7 @@
 		this.options = options || {};
 		this.interlanguageList = {};
 		this.compactList = {};
+		this.commonInterlanguageList = null;
 		this.$trigger = null;
 		this.compactSize = 0;
 		this.listSize = 0;
@@ -175,7 +176,7 @@
 				compact: true,
 				languages: ulsLanguageList,
 				// Show common languages
-				quickList: self.filterByCommonLanguages( languages )
+				quickList: self.getCommonLanguages( languages )
 			} );
 		},
 
@@ -234,7 +235,7 @@
 
 				// Add all common languages to the beginning of array.
 				// These are the most probable languages predicted by ULS.
-				this.filterByCommonLanguages( languages ),
+				this.getCommonLanguages( languages ),
 
 				// Finally add the whole languages array too.
 				// We will remove duplicates and cut down to required size.
@@ -320,6 +321,13 @@
 			return interlanguageList;
 		},
 
+		/**
+		 * Get common languages - the most probable languages predicted by ULS.
+		 */
+		getCommonLanguages: function ( languages ) {
+			return this.commonInterlanguageList || this.filterByCommonLanguages( languages );
+		},
+
 		/**
 		 * Hide the original interlanguage list
 		 */