Improve generated Proxy code performance

By using a shared handler object, we get the performance increases record in #156 (comment).

Author: ExE-Boss

lib/constructs/interface.js

@@ -582,7 +582,7 @@ class Interface {
     }
   }
 
-  generateLegacyProxy() {
+  generateLegacyProxyHandler() {
     const hasIndexedSetter = this.indexedSetter !== null;
     const hasNamedSetter = this.namedSetter !== null;
     const hasNamedDeleter = this.namedDeleter !== null;
@@ -694,7 +694,7 @@ class Interface {
     };
 
     this.str += `
-      obj = new Proxy(obj, {
+      const proxyHandler = {
     `;
 
     // [[Get]] (necessary because of proxy semantics)
@@ -1094,7 +1094,7 @@ class Interface {
     `;
 
     this.str += `
-      });
+      };
     `;
   }
 
@@ -1142,7 +1142,9 @@ class Interface {
     `;
 
     if (this.isLegacyPlatformObj) {
-      this.generateLegacyProxy();
+      this.str += `
+        obj = new Proxy(obj, proxyHandler);
+      `;
     }
 
     this.str += `
@@ -1456,6 +1458,9 @@ class Interface {
     this.generateExport();
     this.generateIface();
     this.generateInstall();
+    if (this.isLegacyPlatformObj) {
+      this.generateLegacyProxyHandler();
+    }
 
     this.generateMixins();
     this.generateRequires();