Extensions docs: Improve Web Accessible Resources documentation

The docs currently don't comment on what happens if a legal request for a public resource is started by a web site, but gets redirected by an extension to a non-public resource of that extension.

The added string was agreed upon with cdn@ in https://docs.google.com/a/google.com/document/d/1_9fO74A0Us4iefSNu9EBBLuqDynNsuL98Gsysnqvj_A/edit?usp=sharing

Rendered docs with this CL applied: https://chrome-apps-doc.appspot.com/_patch/96713002/extensions/manifest/web_accessible_resources.html

NOTRY=true
BUG=313155

Review URL: https://codereview.chromium.org/96713002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239737 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239737
Updates docked background when shelf is auto-hidden

BUG=267582
TEST=Visual.
Dock a window.
Verify that docked background is same as the launcher background.
Set launcher to auto-hide.
Move mouse pointer to the bottom of the screen.
Verify that both docked background and the shelf animate together.
Verify that there is no overap between the shelf and docked area background.
Verify that there is no gap between the shelf and docked area background.

Review URL: https://codereview.chromium.org/110503005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239738 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239738