Last year we changed the debugger behavior to re-open the secondary pane when paused.

We did this because it is nice to see the call stack. The unintended consequence is when devtools is docked to the right or to the bottom and narrow, the UI can often be cramped. It is frustrating to close the secondary pane and then see it re-open.

Another thing that changed recently is that the command bar buttons are now visible even when the secondary pane is closed, which makes the pane less necessary.

Push with failures: https://treeherder.mozilla.org/#/jobs?repo=autoland&resultStatus=testfailed%2Cbusted%2Cexception&revision=f057b78337e7442427b3379537c67d5761f2bf39&selectedJob=240393765&searchStr=linux%2Cx64%2Copt%2Cnode%2Ctests%2Csource-test-node-debugger-tests%2Cnode%28debugger%29

Failure log: https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=240393765&repo=autoland&lineNumber=801

Backout link: https://hg.mozilla.org/integration/autoland/rev/9c2a65500d3aebbc471d88d5f38676c7433ddb60

[task 2019-04-15T17:32:21.400Z] Error ------------------------------------------------------------------ src/utils/sources-tree/tests/utils.spec.js:51:9
[task 2019-04-15T17:32:21.401Z]
[task 2019-04-15T17:32:21.401Z] Cannot call addToTree because no more than 3 arguments are expected by function [1].
[task 2019-04-15T17:32:21.401Z]
[task 2019-04-15T17:32:21.401Z] src/utils/sources-tree/tests/utils.spec.js:51:9
[task 2019-04-15T17:32:21.401Z] 51| addToTree(tree, source, "http://example.com/", "")
[task 2019-04-15T17:32:21.401Z] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[task 2019-04-15T17:32:21.401Z]
[task 2019-04-15T17:32:21.402Z] References:
[task 2019-04-15T17:32:21.402Z] src/utils/sources-tree/addToTree.js:157:8
[task 2019-04-15T17:32:21.402Z] v------------------
[task 2019-04-15T17:32:21.402Z] 157| export function addToTree(
[task 2019-04-15T17:32:21.402Z] 158| tree: TreeDirectory,
[task 2019-04-15T17:32:21.402Z] 159| source: Source,
[task 2019-04-15T17:32:21.402Z] 160| debuggeeHost: ?string
[task 2019-04-15T17:32:21.402Z] 161| ) {
[task 2019-04-15T17:32:21.403Z] ^ [1]
[task 2019-04-15T17:32:21.403Z]
[task 2019-04-15T17:32:21.403Z]
[task 2019-04-15T17:32:21.403Z]
[task 2019-04-15T17:32:21.403Z] Found 25 errors

https://hg.mozilla.org/mozilla-central/rev/b1d9126436b5