New perf dashboard should have multiple dashboard pages

New perf dashboard should have multiple dashboard pages
https://bugs.webkit.org/show_bug.cgi?id=141339

Reviewed by Chris Dumez.

Added the support for multiple dashboard pages. Also added the status of the latest data point.
e.g. "5% better than target"

* public/v2/app.css: Tweaked the styles to work around the fact Ember.js creates empty script elements.
Also hid the border lines around charts on the dashboard page for a cleaner look.

* public/v2/app.js:
(App.IndexRoute): Added. Navigate to /dashboard/<defaultDashboardName> once the manifest.json is loaded.
(App.IndexRoute.beforeModel): Added.
(App.DashboardRoute): Added.
(App.DashboardRoute.model): Added. Return the dashboard specified by the name.
(App.CustomDashboardRoute): Added. This route is used for a customized dashboard specified by "grid".
(App.CustomDashboardRoute.model): Create a dashboard model from "grid" query parameter.
(App.CustomDashboardRoute.renderTemplate): Use the dashboard template.
(App.DashboardController): Renamed from App.IndexController.
(App.DashboardController.modelChanged): Renamed from gridChanged. Removed the code to deal with "grid"
and "defaultDashboard" as these are taken care of by newly added routers.
(App.DashboardController.computeGrid): Renamed from updateGrid. No longer updates "grid" since this is
now done in actions.toggleEditMode.
(App.DashboardController.actions.toggleEditMode): Navigate to CustomDashboardRoute when start editing
an existing dashboard.

(App.Pane.computeStatus): Moved from App.PaneController so that to be called in App.Pane.latestStatus.
Also moved the code to compute the delta with respect to the previous data point from _updateDetails.
(App.Pane._relativeDifferentToLaterPointInTimeSeries): Ditto.
(App.Pane.latestStatus): Added. Used by the dashboard template to show the status of the latest result.

(App.createChartData): Added deltaFormatter to show less significant digits for differences.

(App.PaneController._updateDetails): Updated per changes to computeStatus.

* public/v2/chart-pane.css: Added style rules for the status labels on the dashboard.

* public/v2/data.js:
(TimeSeries.prototype.lastPoint): Added.

* public/v2/index.html: Prefetch manifest.json as soon as possible, show the latest data points' status
on the dashboard, and enumerate all predefined dashboards.

* public/v2/interactive-chart.js:
(App.InteractiveChartComponent._relayoutDataAndAxes): Slightly adjust the offset at which we show unit
for the dashboard page.

* public/v2/manifest.js:
(App.Dashboard): Inherit from App.NameLabelModel now that each predefined dashboard has a name.
(App.MetricSerializer.normalizePayload): Parse all predefined dashboards instead of a single dashboard.
IDs are generated for each dashboard for forward compatibility.
(App.Manifest):
(App.Manifest.dashboardByName): Added.
(App.Manifest.defaultDashboardName): Added.
(App.Manifest._fetchedManifest): Create dashboard model objects for all predefined ones.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@179763 268f45cc-cd09-0410-ab3c-d52691b4dbfc