Clean up SmbShare build guards for Chrome OS

Adds is_chromeos checks to the build files for the add-smb-share-dialog

Bug: chromium:887135
Change-Id: I7ba729324c9e523f82924927f6eab86be8e4247f
Reviewed-on: https://chromium-review.googlesource.com/c/1323806Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Bailey Berro <baileyberro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606916}

chrome/browser/resources/settings/downloads_page/BUILD.gn

@@ -8,8 +8,10 @@ js_type_check("closure_compile") {
   deps = [
     ":downloads_browser_proxy",
     ":downloads_page",
-    ":smb_shares_page",
   ]
+  if (is_chromeos) {
+    deps += [ ":smb_shares_page" ]
+  }
 }
 
 js_library("downloads_browser_proxy") {
@@ -19,12 +21,14 @@ js_library("downloads_browser_proxy") {
   ]
 }
 
-js_library("smb_shares_page") {
-  deps = [
-    "..:route",
-    "//ui/webui/resources/cr_components/chromeos/smb_shares:smb_browser_proxy",
-    "//ui/webui/resources/js:web_ui_listener_behavior",
-  ]
+if (is_chromeos) {
+  js_library("smb_shares_page") {
+    deps = [
+      "..:route",
+      "//ui/webui/resources/cr_components/chromeos/smb_shares:smb_browser_proxy",
+      "//ui/webui/resources/js:web_ui_listener_behavior",
+    ]
+  }
 }
 
 js_library("downloads_page") {

ui/webui/resources/cr_components/chromeos/smb_shares/BUILD.gn

@@ -4,6 +4,8 @@
 
 import("//third_party/closure_compiler/compile_js.gni")
 
+assert(is_chromeos, "SMB Shares is Chrome OS only.")
+
 js_type_check("closure_compile") {
   deps = [
     ":add_smb_share_dialog",