With the NPAPI deprecation, Adobe have now made a supported, automatically updating version of Pepper Flash available on Windows and OS X.

This CL moves the code previously added in https://codereview.chromium.org/203993004 into chrome/common so the system plugin is added on all Chromium builds.

To manually override bundled PepperFlash on Chrome (e.g. to load a Debug version), use --disable-bundled-ppapi-flash

BUG=345886,454131
TEST=Install PPAPI Flash from Adobe site (link in bug)
TEST=For Chromium builds: Check Chromium now automatically uses system version of Flash in chrome://plugins.
TEST=For Chrome builds: Check Chrome still uses bundled Flash by default.  Check if --disable-bundled-ppapi-flash it uses system flash.
TEST=Check an old version of System flash will pop out of date plugin warning.

Review URL: https://codereview.chromium.org/893823002

Cr-Commit-Position: refs/heads/master@{#317656}