Gallery: Add browser tests to apply the exposure effect for an image.

chrome/test/data/extensions/api_test/file_manager_browsertest/gallery/test_util.js

Index: chrome/test/data/extensions/api_test/file_manager_browsertest/gallery/test_util.js
diff --git a/chrome/test/data/extensions/api_test/file_manager_browsertest/gallery/test_util.js b/chrome/test/data/extensions/api_test/file_manager_browsertest/gallery/test_util.js
index 430f5f84670d9e5fba10df6cdd0e70f797747bf0..f81f6b692168e7cc77ec1995949cbc083789f801 100644
--- a/chrome/test/data/extensions/api_test/file_manager_browsertest/gallery/test_util.js
+++ b/chrome/test/data/extensions/api_test/file_manager_browsertest/gallery/test_util.js
@@ -83,8 +83,9 @@ function launchWithTestEntries(
         selectedEntries.map(function(entry) { return entry.nameText; }));
   });
   return launch(entriesPromise).then(function() {
-    return appWindowPromise.then(function(appWindow) {
-      return {appWindow: appWindow, entries: entries};
+    var launchedPromise = Promise.all([appWindowPromise, entriesPromise]);
+    return launchedPromise.then(function(results) {
+      return {appWindow: results[0], entries: results[1]};
     });
   });
 }