Bug 1299276 - Add a separate --enable-stylo option to control MOZ_STYLO separate from the linkage effects of --with-servo. r=froydnj

toolkit/moz.configure

@@ -497,19 +497,26 @@ simple_keyfile('Adjust SDK')
 
 # Servo integration
 # ==============================================================
+option('--enable-stylo', env='STYLO_ENABLED', nargs=0,
+       help='Enables experimental integration with the servo style system. '
+            'This requires either building servo within Gecko\'s cargo phase '
+            'or passing --with-servo')
+
+@depends('--enable-stylo')
+def stylo(value):
+    return bool(value)
+
+set_define('MOZ_STYLO', stylo)
+imply_option('--enable-jemalloc', depends_if('--enable-stylo')(lambda _: 'moz'))
+
 option('--with-servo', env='SERVO_TARGET_DIR', nargs=1,
        help='Absolute path of the target directory where libgeckoservo can '
-            'be found. This is generally servo_src_dir/target/release.'
-            'Passing this flag enables experimental integration with the '
-            'servo style system')
+            'be found. This is generally servo_src_dir/target/release.')
 
 @depends_if('--with-servo')
 def servo_target_dir(value):
     return value[0]
 
-imply_option('--enable-jemalloc', depends_if('--with-servo')(lambda _: 'moz'))
-
-set_define('MOZ_STYLO', depends_if(servo_target_dir)(lambda x: bool(x)))
 set_config('SERVO_TARGET_DIR', servo_target_dir)
 
 # Gecko integrated IPC fuzzer