Bug 1445780: Part 1 - Allow synthesizeMouse to accept an array of selectors for content in iframes. r=aswan

MozReview-Commit-ID: JCRagaqkkZ6

--HG--
extra : rebase_source : 81d1bd14030b41196c951512c26025e2cf0db9ac

testing/mochitest/BrowserTestUtils/BrowserTestUtils.jsm

@@ -1011,6 +1011,9 @@ var BrowserTestUtils = {
    *        One of the following:
    *        - a selector string that identifies the element to target. The syntax is as
    *          for querySelector.
+   *        - An array of selector strings. Each selector after the first
+   *          selects for an element in the iframe specified by the previous
+   *          selector.
    *        - a CPOW element (for easier test-conversion).
    *        - a function to be run in the content process that returns the element to
    *        target
@@ -1045,7 +1048,7 @@ var BrowserTestUtils = {
       if (typeof target == "function") {
         targetFn = target.toString();
         target = null;
-      } else if (typeof target != "string") {
+      } else if (typeof target != "string" && !Array.isArray(target)) {
         cpowObject = target;
         target = null;
       }

testing/mochitest/tests/SimpleTest/AsyncUtilsContent.js

@@ -25,6 +25,13 @@ addMessageListener("Test:SynthesizeMouse", (message) => {
   if (typeof target == "string") {
     target = content.document.querySelector(target);
   }
+  else if (Array.isArray(target)) {
+    let elem = {contentDocument: content.document};
+    for (let sel of target) {
+      elem = elem.contentDocument.querySelector(sel);
+    }
+    target = elem;
+  }
   else if (typeof data.targetFn == "string") {
     let runnablestr = `
       (() => {