Using grayscale screenshots for GestureNav so that the user can clearly tell when screenshot is shown vs. the live content.

BUG=331895

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=249431

Review URL: https://codereview.chromium.org/136453009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249782 0039d316-1c4b-4281-b951-d872f2087c98
Clean up JS style and separate unrelated functionality.

This change is not intended to have any effect on the
extension's functionality or behavior.

Review URL: https://codereview.chromium.org/149463008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249783 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249783