Minimal set of changes for blink core jumbo build.

third_party/WebKit/Source/core/layout/BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//third_party/WebKit/Source/core/core.gni")
 
 blink_core_sources("layout") {
   split_count = 5
 
   sources = [
@@ skipping 448 matching lines @@
     ]
   }
 
   if (is_android) {
     sources += [
       "LayoutThemeAndroid.cpp",
       "LayoutThemeAndroid.h",
     ]
   }
 
+  jumbo_excluded_sources = [
+    # Collides with CompositedLayerMapping.cpp (patch incoming)
+    "compositing/CompositingLayerAssigner.cpp",
+  ]
+
   configs += [
     # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
     "//build/config/compiler:no_size_t_to_int_warning",
   ]
 }