Browser Plugin: Remove Zoom

With the zoom refactor in flight: https://codereview.chromium.org/287093002/, zoom
plumbing for BrowserPlugin in the content layer is now entirely dead code. We need to revisit zoom in
the chrome layer for <webview> so that the embedder's zoom is propagated to the guests.

This will be done at a later time when we need to get <webview> in WebUI working again.

BUG=330264
TBR=jam@chromium.org for trivial browser_plugin_guest_delegate.h code deletion.

Review URL: https://codereview.chromium.org/303423002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@273959 0039d316-1c4b-4281-b951-d872f2087c98
7 files changed