Leverage ResourceBundle::IsGzipped from resource_bundle_source_map.cc

Previously extensions::Dispatcher::GetJsResources() relied on a manually
specified boolean which had to be kept in sync with a grd file's
compress="gzip" attributes (only leveraged by IDR_MOJO_MOJO_BINDINGS_JS).

This is no longer necessary since ResourceBundle::IsGzipped() can be used
to determine if the file is gzipped or not.

Basically this CL undoes a subset of the changes introduced at r516811.

Bug: 961063
Change-Id: I03740235f2c0ee62c9f406be336fa524e89d2d6a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1602132
Auto-Submit: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659277}
4 files changed