Bug 1065185 - Fix devtools actors. r=bz

See browser/devtools/canvasdebugger/test/browser_canvas-actor-test-02.js.
And note that we need to re-waive the result, otherwise we get failures in
browser/devtools/canvasdebugger/test/browser_canvas-actor-test-10.js.

See browser/devtools/shadereditor/test/browser_se_editors-contents.js for the
webgls stuff.

toolkit/devtools/server/actors/call-watcher.js

@@ -412,11 +412,13 @@ let CallWatcherActor = exports.CallWatcherActor = protocol.ActorClass({
      * Instruments a function on the specified target object.
      */
     function overrideFunction(global, target, name, descriptor, callback) {
-      let originalFunc = target[name];
+      // Invoking .apply on an unxrayed content function doesn't work, because
+      // the arguments array is inaccessible to it. Get Xrays back.
+      let originalFunc = Cu.unwaiveXrays(target[name]);
 
       Object.defineProperty(target, name, {
         value: function(...args) {
-          let result = originalFunc.apply(this, args);
+          let result = Cu.waiveXrays(originalFunc.apply(this, args));
 
           if (self._recording) {
             let stack = getStack(name);
@@ -435,13 +437,15 @@ let CallWatcherActor = exports.CallWatcherActor = protocol.ActorClass({
      * Instruments a getter or setter on the specified target object.
      */
     function overrideAccessor(global, target, name, descriptor, callback) {
-      let originalGetter = target.__lookupGetter__(name);
-      let originalSetter = target.__lookupSetter__(name);
+      // Invoking .apply on an unxrayed content function doesn't work, because
+      // the arguments array is inaccessible to it. Get Xrays back.
+      let originalGetter = Cu.unwaiveXrays(target.__lookupGetter__(name));
+      let originalSetter = Cu.unwaiveXrays(target.__lookupSetter__(name));
 
       Object.defineProperty(target, name, {
         get: function(...args) {
           if (!originalGetter) return undefined;
-          let result = originalGetter.apply(this, args);
+          let result = Cu.waiveXrays(originalGetter.apply(this, args));
 
           if (self._recording) {
             let stack = getStack(name);

toolkit/devtools/server/actors/webgl.js

@@ -492,7 +492,9 @@ let WebGLInstrumenter = {
         if (glBreak) return undefined;
       }
 
-      let glResult = originalFunc.apply(this, glArgs);
+      // Invoking .apply on an unxrayed content function doesn't work, because
+      // the arguments array is inaccessible to it. Get Xrays back.
+      let glResult = Cu.waiveXrays(Cu.unwaiveXrays(originalFunc).apply(this, glArgs));
 
       if (timing >= 0 && !observer.suppressHandlers) {
         let glBreak = observer[afterFuncName](glArgs, glResult, cache, proxy);