Don't compile app_icon_factory except for ChromeOS.

Compiling app_icon_factory  code triggered compilation errors in some
Windows and Mac builds since the code references app_list which
only exists in ChromeOS. In most builds it was ok because the generated
object file was unused and got stripped by the linker before the dangling
references was found.

BUG=826982

TBR=nigeltao@chromium.org,rdevlin.cronin@chromium.org,dominickn@chromium.org

Change-Id: I25f0fa090f3466bcc83e06a070c7aa6c8600976d
Reviewed-on: https://chromium-review.googlesource.com/c/1373450Reviewed-by: Daniel Bratell <bratell@opera.com>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#615856}

chrome/browser/BUILD.gn

@@ -2589,8 +2589,6 @@ jumbo_split_static_library("browser") {
     sources += [
       "accessibility/invert_bubble_prefs.cc",
       "accessibility/invert_bubble_prefs.h",
-      "apps/app_service/app_icon_factory.cc",
-      "apps/app_service/app_icon_factory.h",
       "apps/app_service/app_icon_source.cc",
       "apps/app_service/app_icon_source.h",
       "apps/app_service/app_service_proxy.cc",
@@ -3121,6 +3119,8 @@ jumbo_split_static_library("browser") {
 
   if (is_chromeos) {
     sources += [
+      "apps/app_service/app_icon_factory.cc",
+      "apps/app_service/app_icon_factory.h",
       "apps/app_service/built_in_chromeos_apps.cc",
       "apps/app_service/built_in_chromeos_apps.h",
       "apps/app_service/extension_apps.cc",