Don't record Prerender PLT measurements when the PrerenderManager is disabled.
Don't record Prerender PLT measurements when the PrerenderManager is disabled.

BUG=77783
TEST=Disable prerender and make sure that histograms do not show up. Enable and make sure it does.

Review URL: http://codereview.chromium.org/6670125

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@80048 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser