cros: Use lazy serialization for window service mojo methods

The window service runs in the browser process for --mus and in the
ash_and_ui process for --mash. Use the support_lazy_serialization
build flag for the window service mojom targets so that in-process
mojo method calls avoid doing serialization for IPC. This should
improve event dispatch performance, as the mojo call becomes
equivalent to a PostTask.

This causes a known 130KB code size increase on 64-bit Intel
builds, so the feature is enabled on Chrome OS only.

Bug: 798800
Test: bots
Change-Id: Ia488f95e6dd35ce1947df7117e623cd222786fb0
Reviewed-on: https://chromium-review.googlesource.com/849657Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#526999}

services/ui/public/interfaces/BUILD.gn

@@ -6,6 +6,14 @@ import("//mojo/public/tools/bindings/mojom.gni")
 import("//testing/test.gni")
 
 mojom("interfaces") {
+  # The window service runs in the browser process for --mus and in the
+  # ash_and_ui process for --mash. Allow IPC serialization to be skipped for
+  # the common case of in-process mojo calls. This causes a ~130KB size
+  # increase on 64-bit Intel builds.
+  if (is_chromeos) {
+    support_lazy_serialization = true
+  }
+
   sources = [
     "accessibility_manager.mojom",
     "clipboard.mojom",

services/ui/public/interfaces/ime/BUILD.gn

@@ -5,6 +5,11 @@
 import("//mojo/public/tools/bindings/mojom.gni")
 
 mojom("ime") {
+  # See //services/ui/public/interfaces/BUILD.gn
+  if (is_chromeos) {
+    support_lazy_serialization = true
+  }
+
   sources = [
     "ime.mojom",
   ]