[Devtools] Do not switch tabs by default when adding a tab.

[Devtools] Do not switch tabs by default when adding a tab.

If the user has not selected a default tab, TimelineDetailsView's
_lastUserSelectedTabId will be undefined which will cause appendTab
to select the last added tab by default. This patch changes this
behavior to not select the most recently added tab. This can be seen
in the paint profiler where the paint tab takes precedence over the
details tab. With this patch, the details tab is shown by default.

TEST=manual. By default the paint tab is not selected on the timeline.
BUG=410701

[pdr., 2014-10-06 04:28:38]

pdr@chromium.org changed reviewers:
+ caseq@chromium.org, yurys@chromium.org

[pfeldman, 2014-10-06 04:56:14]

pfeldman@chromium.org changed reviewers:
+ pfeldman@chromium.org

[pfeldman, 2014-10-06 04:56:15]

https://codereview.chromium.org/627413002/diff/1/Source/devtools/front_end/ti...
File Source/devtools/front_end/timeline/TimelinePanel.js (right):

https://codereview.chromium.org/627413002/diff/1/Source/devtools/front_end/ti...
Source/devtools/front_end/timeline/TimelinePanel.js:1175: if
(this._lastUserSelectedTabId && this._lastUserSelectedTabId !==
this.selectedTabId)
Is (was) this showing all the tabs as they were added? I wonder if we should
turn the control flow the other way around so that this details view was
listening to the timeline selection and was updating itself. That way it can
manage the tab selection properly.

The way it is now is because this details view was created out of the popover
that used to show upon timeline hover. Hence the suboptimal way of living.

@pdr: you don't have to do this, we can arrange this for you!