Merge M45: Remove NPAPI command line flags entirely.

ContentShell now overrides IsNpapiEnabled() to enable NPAPI for testing.

BUG=493212
CQ_INCLUDE_TRYBOTS=tryserver.blink:win_blink_rel,mac_blink_rel

Review URL: https://codereview.chromium.org/1240543003

Cr-Commit-Position: refs/heads/master@{#339469}
(cherry picked from commit 6be0628ff61f6ffd12d686caddb8c522e10824a9)

Review URL: https://codereview.chromium.org/1248363003 .

Cr-Commit-Position: refs/branch-heads/2454@{#113}
Cr-Branched-From: 12bfc3360892ec53cd00fc239a47e5298beb063b-refs/heads/master@{#338390}
9 files changed