Move global V8::UseCrankshaft() into the Isolate.

R=jkummerow@chromium.org
BUG=v8:2744

Review URL: https://codereview.chromium.org/23441029

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16494 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix interceptor handling in crankshaft.

R=dcarney@chromium.org

Review URL: https://chromiumcodereview.appspot.com/23614011

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16495 ce2b1a6d-e550-0410-aec6-3dcde31c8c00