Bug 1268981 - Make sure the bfcache is enabled during the mobile session store form data test. r=margaret

Without the bfcache, the inner value will not be restored after a page navigation, therefore we need to make sure that the bfcache isn't disabled by a stray memory pressure event before or during the test.

MozReview-Commit-ID: 3k1EgGDEPb

--HG--
extra : transplant_source : %E7%C9%BCD%E3%A4P%7F%A8%04%F4%CE%96bw%D6PU%97%01

mobile/android/app/mobile.js

@@ -135,6 +135,7 @@ pref("browser.display.remotetabs.timeout", 10);
 pref("browser.sessionhistory.max_total_viewers", 1);
 pref("browser.sessionhistory.max_entries", 50);
 pref("browser.sessionhistory.contentViewerTimeout", 360);
+pref("browser.sessionhistory.bfcacheIgnoreMemoryPressure", false);
 
 /* session store */
 pref("browser.sessionstore.resume_session_once", false);

mobile/android/chrome/content/MemoryObserver.js

@@ -37,7 +37,9 @@ var MemoryObserver = {
     defaults.setIntPref("image.mem.max_decoded_image_kb", 0);
 
     // Stop using the bfcache
-    defaults.setIntPref("browser.sessionhistory.max_total_viewers", 0);
+    if (!Services.prefs.getBoolPref("browser.sessionhistory.bfcacheIgnoreMemoryPressure")) {
+      defaults.setIntPref("browser.sessionhistory.max_total_viewers", 0);
+    }
   },
 
   zombify: function(tab) {

mobile/android/tests/browser/chrome/test_session_form_data.html

@@ -193,6 +193,17 @@ add_task(function* test_formdata_navigation() {
   const OUTER_VALUE = "browser_formdata_" + Math.random();
   const INNER_VALUE = "browser_formdata_" + Math.random();
 
+  // Make sure the bfcache remains enabled during this test,
+  // otherwise the inner value will not be restored correctly.
+  Services.prefs.setBoolPref("browser.sessionhistory.bfcacheIgnoreMemoryPressure", true);
+  Services.prefs.setIntPref("browser.sessionhistory.max_total_viewers", 1);
+
+  SimpleTest.registerCleanupFunction(function() {
+    // Turn the bfcache memory pressure protection back off once we're finished.
+    Services.prefs.clearUserPref("browser.sessionhistory.bfcacheIgnoreMemoryPressure");
+    Services.prefs.clearUserPref("browser.sessionhistory.max_total_viewers");
+  });
+
   // Creates a tab, loads a page with some form fields, modifies their values,
   // navigates to a different page and back again and closes the tab.
   function createNavigateAndRemoveTab() {