Bug 1292197, Bug 1289087, Bug 1283703, Bug 1283702, Bug 1283701, Bug 1283700, Bug 1283699 - Add requestLongerTimeout for slow memory tests; r=jimb

Pretty much all of the browser mochitests for the memory panel have very
infrequent (about once a month) timeouts. In every case, the test has not hung
and just sat there, but is still actively doing work and just loses the race
against the timeout timer by fractions of a second. Ideally, we would speed up
the tests, but given that we already use small (in terms of heap size) test
cases and do as many analyses as we can in parallel, I think the best we can do
is increase the timeout threshold for these problematic tests.

--HG--
extra : amend_source : 5d47921db619ca0e5c666e98f708c8df9700c816

devtools/client/memory/test/browser/head.js

@@ -56,6 +56,10 @@ function makeMemoryTest(url, generator) {
   return Task.async(function* () {
     waitForExplicitFinish();
 
+    // It can take a long time to save a snapshot to disk, read the snapshots
+    // back from disk, and finally perform analyses on them.
+    requestLongerTimeout(2);
+
     const tab = yield addTab(url);
     const results = yield openMemoryPanel(tab);