DevTools: kill WI.SourcesView._showFile method

The patch slightly untangles WI.SourcesView from WI.TabbedEditorContainer
so that they don't jump to and fro to open a file in a tab.

BUG=none
R=pfeldman, dgozman

Review-Url: https://codereview.chromium.org/2152293002
Cr-Commit-Position: refs/heads/master@{#405862}
2 files changed