extensions: Fix doc generation for tabs.captureVisibleTab.

Private apis are not documented, so move the private ImageDetails definition
into chrome.types, so that the documentation can be updated correctly.

BUG=327424
R=kalman@chromium.org

Review URL: https://codereview.chromium.org/110633004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240001 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240001
rAc: change sandbox server wording

BUG=327533
TBR=thestig@chromium.org

Review URL: https://codereview.chromium.org/106423009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240002 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240002