Merge pull request #2237 from abarth/fix_build

The build failed without Firebase

sky/services/firebase/BUILD.gn

@@ -7,12 +7,16 @@
 
 import("//mojo/public/tools/bindings/mojom.gni")
 
+declare_args() {                                                                
+  enable_firebase = false                                                 
+}
+
 group("firebase") {
   deps = [
     ":interfaces",
   ]
 
-  if (is_ios || is_android) {
+  if (enable_firebase && (is_ios || is_android)) {
     deps += [ ":firebase_lib" ]
   }
 }
@@ -23,6 +27,8 @@ mojom("interfaces") {
   ]
 }
 
+if (enable_firebase) {
+
 if (is_android) {
   import("//build/config/android/config.gni")
   import("//build/config/android/rules.gni")
@@ -81,3 +87,5 @@ if (is_ios) {
     ]
   }
 }
+
+}