Factor DocumentSubresourceFilter out of SubresourceFilterAgent.

components/subresource_filter.gypi

Index: components/subresource_filter.gypi
diff --git a/components/subresource_filter.gypi b/components/subresource_filter.gypi
index 2e347cd197a9383faff640a93a8ac149828e2798..f437d643a1919bd85adffa4e9193d3d2c539b153 100644
--- a/components/subresource_filter.gypi
+++ b/components/subresource_filter.gypi
@@ -112,6 +112,23 @@
       },
       'includes': [ '../build/protoc.gypi' ],
     },
+    {
+      # GN version: //components/subresource_filter/core/common:test_support
+      'target_name': 'subresource_filter_core_common_test_support',
+      'type': 'static_library',
+      'dependencies': [
+        '../base/base.gyp:base',
+        '../testing/gtest.gyp:gtest',
+      ],
+      'include_dirs': [
+        '..',
+      ],
+      'sources': [
+        # Note: sources list duplicated in GN build.
+        'subresource_filter/core/common/test_ruleset_creator.cc',
+        'subresource_filter/core/common/test_ruleset_creator.h',
+      ],
+    },
   ],
   'conditions': [
     ['OS != "ios"', {
@@ -152,6 +169,8 @@
           ],
           'sources': [
             # Note: sources list duplicated in GN build.
+            'subresource_filter/content/renderer/document_subresource_filter.cc',
+            'subresource_filter/content/renderer/document_subresource_filter.h',
             'subresource_filter/content/renderer/ruleset_dealer.cc',
             'subresource_filter/content/renderer/ruleset_dealer.h',
             'subresource_filter/content/renderer/subresource_filter_agent.cc',