Create --disable-extensions-except switch

In response to users/developers using --disable-extensions to disable all
extensions except the ones loaded as components, --load-component-extension.

Create a --disable-extensions-except switch, which disables all extensions that
are not specified, but treats the listed extensions as normal extensions.

BUG=615096

Review-Url: https://codereview.chromium.org/2166513002
Cr-Commit-Position: refs/heads/master@{#415462}
7 files changed