Refactored instances of "web_contents()" to "guest_web_contents()" in webview_guest.cc for consistency.

BUG=

Review URL: https://codereview.chromium.org/134203003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246953 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246953
Disk cache v3: Improve the skeleton of BackendImpl and EntryImpl.

The idea is to start adding code slowly to make reviews easier.
Nothing significant is changing here.

BUG=241277
TEST=none

Review URL: https://codereview.chromium.org/64293007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246954 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246954