Remove references to extensions from //components/guest_view/.

We had an assert(enable_extensions) in //components/guest_view/ to
prevent the accidental building of GuestViews on mobile, since
extensions are currently the only thing using GuestViews. However,
referencing extensions here violates layering.

This modifies the assert to not reference extensions.

BUG=726694

Review-Url: https://codereview.chromium.org/2907863002
Cr-Commit-Position: refs/heads/master@{#475554}

components/BUILD.gn

@@ -5,7 +5,6 @@
 import("//build/config/chrome_build.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
-import("//extensions/features/features.gni")
 import("//printing/features/features.gni")
 import("//rlz/features/features.gni")
 import("//testing/test.gni")
@@ -161,10 +160,6 @@ test("components_unittests") {
     deps += [ "//components/nacl/browser:unit_tests" ]
   }
 
-  if (enable_extensions) {
-    deps += [ "//components/guest_view/browser:unit_tests" ]
-  }
-
   if (is_ios) {
     deps += [
       "//components/image_fetcher/ios:unit_tests",
@@ -281,6 +276,10 @@ test("components_unittests") {
     deps += [
       "//components/cryptauth:unit_tests",
       "//components/feedback:unit_tests",
+
+      # See comment in components/guest_view/browser/BUILD.gn for why
+      # guest_view is currently non-mobile.
+      "//components/guest_view/browser:unit_tests",
       "//components/proximity_auth:unit_tests",
       "//components/storage_monitor:unit_tests",
       "//components/web_modal:unit_tests",

components/guest_view/browser/BUILD.gn

@@ -2,9 +2,11 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//extensions/features/features.gni")
-
-assert(enable_extensions)
+# Currently, GuestViews are only used by extensions, so we have this
+# assert to prevent the accidental building of GuestViews on mobile
+# platforms. If you're now using GuestViews on mobile, go ahead and
+# remove this assert.
+assert(!is_android && !is_ios)
 
 static_library("browser") {
   output_name = "guest_view_browser"

components/guest_view/renderer/BUILD.gn

@@ -2,9 +2,11 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//extensions/features/features.gni")
-
-assert(enable_extensions)
+# Currently, GuestViews are only used by extensions, so we have this
+# assert to prevent the accidental building of GuestViews on mobile
+# platforms. If you're now using GuestViews on mobile, go ahead and
+# remove this assert.
+assert(!is_android && !is_ios)
 
 static_library("renderer") {
   sources = [