DevTools: Make node screenshot pass coordinates in dip.
DevTools: Make node screenshot pass coordinates in dip.

BUG=786993

Change-Id: I4b796f74df16fb6352f7c844d7390935b8b8ef71
Reviewed-on: https://chromium-review.googlesource.com/c/1410316
Commit-Queue: Alexei Filippov <52e51c43e283548b762e3c9dd9a4600768db9fb4@chromium.org>
Reviewed-by: Dmitry Gozman <0ca14b32cbb359a30ac562af27dd84cc2813eacb@chromium.org>
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#623107}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 7f5f19d3f1dafefab02d1ce64781c4098c158db4
ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend