Clean up NativeViewId bits.
Clean up NativeViewId bits.

(Prompted by Stuart's recent work on cleaning up NPAPI bits.)

Review URL: http://codereview.chromium.org/1997005

git-svn-id: http://src.chromium.org/svn/trunk/src@46628 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: c83d16c6a93523537888b9239216785d303619e0
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser