DevTools: NetworkPanel: add hide columns button.

Discussion document:
https://docs.google.com/a/google.com/document/d/1J5us0qToSCqOQ_xSqmEBiL7elhb9tFOjJs7oPBZHhZU

BUG=435984

Review URL: https://codereview.chromium.org/753103002

git-svn-id: svn://svn.chromium.org/blink/trunk@186124 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: [SSP] make createRuleOriginNode static method

ComputedStylePropertiesSection should not rely on StylePropertySection
objects from Styles sidebar pane for its own rendering. This is the
first step to break strong coupling between StylesSidebarPane and
ComputedPropertiesSidebarPane.

R=vsevik

Review URL: https://codereview.chromium.org/768563002

git-svn-id: svn://svn.chromium.org/blink/trunk@186126 bbb929c8-8fbe-4397-9dbb-9b2b20218538