Implement state cookie support for WebInspector.TimelineSidebarPanel.

https://bugs.webkit.org/show_bug.cgi?id=126921

Reviewed by Joseph Pecoraro.

* UserInterface/DebuggerSidebarPanel.js:
(WebInspector.DebuggerSidebarPanel.prototype.restoreStateFromCookie):
Drive-by fix to pass along relaxedMatchDelay to the superclass.

* UserInterface/Main.js:
(WebInspector.loaded):
(WebInspector._provisionalLoadStarted):
Listen for ProvisionalLoadStarted instead of ProvisionalLoadCommitted to save the cookie
before the TimelineRecording is reset and clears the UI.

* UserInterface/NavigationSidebarPanel.js:
(WebInspector.NavigationSidebarPanel.prototype.get restoringState): Added.
(WebInspector.NavigationSidebarPanel.prototype.restoreStateFromCookie.finalAttemptToRestoreViewStateFromCookie):
Delete _pendingViewStateCookie since this was the final attempt.
(WebInspector.NavigationSidebarPanel.prototype.restoreStateFromCookie):
(WebInspector.NavigationSidebarPanel.prototype._isTreeElementWithoutRepresentedObject): Block string represented objects.
(WebInspector.NavigationSidebarPanel.prototype._checkElementsForPendingViewStateCookie):

* UserInterface/OverviewTimelineView.js:
(WebInspector.OverviewTimelineView.prototype._treeElementSelected):

* UserInterface/ResourceSidebarPanel.js:
(WebInspector.ResourceSidebarPanel.prototype.treeElementForRepresentedObject):
Drive-by fix to null check parentFrame since it can be null. Was causing an exception while working on this.

* UserInterface/SourceCodeTimeline.js:
(WebInspector.SourceCodeTimeline):
(WebInspector.SourceCodeTimeline.prototype.saveIdentityToCookie):

* UserInterface/TimelineSidebarPanel.js:
(WebInspector.TimelineSidebarPanel.prototype.canShowDifferentContentView):
(WebInspector.TimelineSidebarPanel.prototype.saveStateToCookie):
(WebInspector.TimelineSidebarPanel.prototype.restoreStateFromCookie):

* UserInterface/TreeOutline.js:
(TreeOutline.prototype._forgetTreeElement):
Drive-by fix to clear selectedTreeElement if it is removed from the tree. Was causing removed TreeElements to be
saved as a cookie since it was still the selected item.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@162413 268f45cc-cd09-0410-ab3c-d52691b4dbfc