Reland "Build non-official app_shell installer on Linux"

This reverts commit 59685821
to reland commit ebc4d82a.

The BUILD.gn file has been updated to use the correct output name
("chromium-app-shell-*" instead of "google-app-shell-*") to fix the
"confirm compile no-op" step on non-official builders.

Original change's description:
> Build non-official app_shell installer on Linux
>
> This causes the app_shell .deb installer to be built on non-ASAN/MSAN
> Linux CQ and waterfall bots, so regressions that break the installer
> build can be caught before hitting the official builders.
>
> The Chrome installer was enabled for non-official Linux builders in
> https://bugs.chromium.org/p/chromium/issues/detail?id=758654#c32.
>
> Bug: 714465
> Change-Id: Ifb6908b756d9ffc292fc131396c424d66f841a2a
> Reviewed-on: https://chromium-review.googlesource.com/956756
> Reviewed-by: Michael Moss <mmoss@chromium.org>
> Commit-Queue: Michael Giuffrida <michaelpg@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#542382}

Bug: 714465
Change-Id: I63b76c36cd8552b39bc7eb0c85808af31758115b
Reviewed-on: https://chromium-review.googlesource.com/961802Reviewed-by: Michael Moss <mmoss@chromium.org>
Commit-Queue: Michael Giuffrida <michaelpg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543132}

extensions/shell/installer/BUILD.gn

@@ -10,9 +10,8 @@ import("//extensions/buildflags/buildflags.gni")
 assert(enable_extensions)
 
 declare_args() {
-  enable_app_shell_installer =
-      is_desktop_linux && is_chrome_branded && current_cpu == "x64" &&
-      !is_component_build && !using_sanitizer
+  enable_app_shell_installer = is_desktop_linux && current_cpu == "x64" &&
+                               !is_component_build && !using_sanitizer
 }
 
 # Meta-target that forwards to the installer of the correct type (if any).

extensions/shell/installer/linux/BUILD.gn

@@ -174,11 +174,18 @@ template("linux_package") {
   action(deb_target_name) {
     visibility = [ ":*" ]
     script = "//build/gn_run_binary.py"
+
+    assert(current_cpu == "x64", "app_shell installer only supported for amd64")
     deb_arch = "amd64"
+    if (is_chrome_branded) {
+      package = "google-app-shell"
+    } else {
+      package = "chromium-app-shell"
+    }
 
     inputs = packaging_files_binaries
     outputs = [
-      "$root_out_dir/google-app-shell-${channel}_${chrome_version_full}-1_${deb_arch}.deb",
+      "$root_out_dir/${package}-${channel}_${chrome_version_full}-1_${deb_arch}.deb",
     ]
 
     args = [