[HBD] Merge two identical ShouldUseJavaScriptSettingForPlugin impls

We are probably going to change this soon to only use the Plugin
content setting for Flash. Before that, we should merge these two
identical implementations so we don't have to change it in two places.

BUG=615738

Review-Url: https://codereview.chromium.org/2367553002
Cr-Commit-Position: refs/heads/master@{#420666}
5 files changed