[foozzie] Fix float array mocks

NOTRY=true

Change-Id: If4dcecf179b955c756a4af468e614b3292f1e5fe
Reviewed-on: https://chromium-review.googlesource.com/522606Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45686}

tools/foozzie/v8_mock.js

@@ -94,8 +94,14 @@ Object.defineProperty(
   var mock = function(arrayType) {
     var handler = {
       construct: function(target, args) {
-        return new Proxy(
-            Function.prototype.bind.apply(arrayType, [null].concat(args)), {});
+        var obj = new (Function.prototype.bind.apply(arrayType, [null].concat(args)));
+        return new Proxy(obj, {
+          get: function(x, prop) {
+            if (typeof x[prop] == "function")
+              return x[prop].bind(obj)
+            return x[prop];
+          },
+        });
       },
     };
     return new Proxy(arrayType, handler);