fix($compile): fix memory leak

For functions that have a '&' binding on the scope, change the function
from an inline definition to an external definition so the function
closure has no access to the parent scope.
Backport of fix on 1.3.x

Closes angular#6794

src/ng/compile.js

@@ -1462,9 +1462,7 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
 
               case '&':
                 parentGet = $parse(attrs[attrName]);
-                isolateScope[scopeName] = function(locals) {
-                  return parentGet(scope, locals);
-                };
+                isolateScope[scopeName] = parentGetFn(parentGet, scope);
                 break;
 
               default:
@@ -1809,8 +1807,19 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
         });
       }
     }
-
-
+	/**
+	 * Wrapper for '&' One-way binding to prevent memory leak.
+	 * Backport from 1.3.x fix for bug #6794.
+	 * @param {function} parentGet Gets value from parent
+	 * @param {ng.$rootScope.Scope} scope Target Scope
+	 * @return {function} & Binding Fn
+	 */
+	function parentGetFn(parentGet, scope) {
+      return function (locals) {
+        return parentGet(scope, locals);
+      };
+    }
+
     function getTrustedContext(node, attrNormalizedName) {
       if (attrNormalizedName == "srcdoc") {
         return $sce.HTML;