Lacros: Make condition of is_chromeos_lacros tighter.

This change makes is_chromeos_lacros to be true only when current_os
is either linux or chromeos. This ensures that is_chromeos_lacros will
evaluate to false when generating ninja files for toolchains such as the
toolchain for pnacl.

It also ensure that enable_scrambled_message_ids is false for
lacros-chrome regardless of toolchain that is in use.

BUG: 1052397
Change-Id: Ibbe8d2149937b506c6c86f2422a356c5d2d4d869
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2581632
Commit-Queue: Yuta Hijikata <ythjkt@chromium.org>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837409}

build/config/chromeos/ui_mode.gni

@@ -23,11 +23,17 @@ declare_args() {
   also_build_ash_chrome = false
 }
 
-# is_chromeos_ash|lacros is used to specify that it is specific to either
+# is_chromeos_{ash,lacros} is used to specify that it is specific to either
 # ash or lacros chrome for chromeos. For platform specific logic that
 # applies to both, use is_chromeos instead.
+# .gn files are evaluated multiple times for each toolchain.
+# is_chromeos_{ash,lacros} should be set true only for builds with target
+# toolchains.
 is_chromeos_ash = is_chromeos && !chromeos_is_browser_only
-is_chromeos_lacros = chromeos_is_browser_only
+
+# TODO(crbug.com/1052397): Remove is_linux once lacros-chrome switches
+# to target_os=chromeos
+is_chromeos_lacros = (is_chromeos || is_linux) && chromeos_is_browser_only
 
 # TODO(crbug.com/1052397):
 # Remove is_ash|lacros once all are replaced by is_chromeos_*.

mojo/public/tools/bindings/mojom.gni

@@ -64,12 +64,15 @@ declare_args() {
 # ARC) we have to explicitly opt out there even when NaCl is enabled (and
 # consequently also when building for NaCl toolchains.) For this reason we
 # check |target_os| explicitly, as it's consistent across all toolchains.
+#
+# TODO(crbug.com/1052397): Remove !chromeos_is_browser_only once
+# lacros-chrome switches to target_os="chromeos"
 enable_scrambled_message_ids =
     enable_mojom_message_id_scrambling &&
     (is_mac || is_win ||
      (is_linux && !is_chromeos_ash && !is_chromecast && !is_chromeos_lacros) ||
      ((enable_nacl || is_nacl || is_nacl_nonsfi) &&
-      (target_os != "chromeos" && !is_chromeos_lacros)))
+      (target_os != "chromeos" && !chromeos_is_browser_only)))
 
 _mojom_tools_root = "//mojo/public/tools"
 _mojom_library_root = "$_mojom_tools_root/mojom/mojom"