Add fromSurface optional parameter to devtools Page.CaptureScreenshot

This allows headless screenshots to work more consistently in all platforms by getting screenshots from the surface rather than the view. It also fixes screenshots not working properly in headless Mac, due to screen dependency.
BUG=687407

Review-Url: https://codereview.chromium.org/2732923002
Cr-Commit-Position: refs/heads/master@{#456309}
8 files changed