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The IPC still needs to be sent because it's used by the webview permission helper to permit PPAPI plugins to run inside a webview.

Remove all the code that backed this, including UMA actions, and a test.  The NPAPI purge, begun, it has.

BUG=439972

Review URL: https://codereview.chromium.org/801053003

Cr-Commit-Position: refs/heads/master@{#308433}