Bug 833877: Add a way to report exceptions in promises. r=Mossop

lib/sdk/core/promise.js

@@ -9,6 +9,13 @@
     factory.call(this, require, exports, module);
   } else if (~String(this).indexOf('BackstagePass')) { // JSM
     this[factory.name] = {};
+    try {
+      this.console = this['Components'].utils
+          .import('resource://gre/modules/devtools/Console.jsm', {}).console;
+    }
+    catch (ex) {
+      // Avoid failures on different toolkit configurations.
+    }
     factory(function require(uri) {
       var imports = {};
       this['Components'].utils.import(uri, imports);
@@ -53,7 +60,12 @@ function attempt(f) {
   **/
   return function effort(options) {
     try { return f(options) }
-    catch(error) { return rejection(error) }
+    catch(error) {
+      if (exports._reportErrors && typeof(console) === 'object') {
+        console.error(error)
+      }
+      return rejection(error)
+    }
   }
 }