Use the pylint checked into depot_tools rather than auto-installing it.

This involves a little hoop-jumping to figure out where depot_tools
actually is. There's a script to do that, but of course that script
isn't under webkitpy, so then we have to find the script and import that :). 

R=eseidel@chromium.org, ojan@chromium.org
BUG=230706

Review URL: https://chromiumcodereview.appspot.com/19491003

git-svn-id: svn://svn.chromium.org/blink/trunk@154450 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove two more dead members from Page.

m_defersLoadingCallCount and m_userStyleSheetModificationTime are set
but never read. As a bonus, also gets rid of an OS(SOLARIS) guard.

BUG=none

Review URL: https://chromiumcodereview.appspot.com/19664003

git-svn-id: svn://svn.chromium.org/blink/trunk@154451 bbb929c8-8fbe-4397-9dbb-9b2b20218538