Factor DocumentSubresourceFilter out of SubresourceFilterAgent.

components/subresource_filter/content/renderer/BUILD.gn

Index: components/subresource_filter/content/renderer/BUILD.gn
diff --git a/components/subresource_filter/content/renderer/BUILD.gn b/components/subresource_filter/content/renderer/BUILD.gn
index 7af2f1085e6bac0c290aee5c959a914ecfec0d6c..b46e8d8251bfecf3079b9120fe8c7d3e6fc93684 100644
--- a/components/subresource_filter/content/renderer/BUILD.gn
+++ b/components/subresource_filter/content/renderer/BUILD.gn
@@ -4,6 +4,8 @@
 
 source_set("renderer") {
   sources = [
+    "document_subresource_filter.cc",
+    "document_subresource_filter.h",
     "ruleset_dealer.cc",
     "ruleset_dealer.h",
     "subresource_filter_agent.cc",
@@ -16,5 +18,27 @@ source_set("renderer") {
     "//content/public/common",
     "//content/public/renderer",
     "//ipc",
+    "//third_party/WebKit/public:blink",
+  ]
+}
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "document_subresource_filter_unittest.cc",
+    "subresource_filter_agent_unittest.cc",
+  ]
+  deps = [
+    ":renderer",
+    "//base",
+    "//components/subresource_filter/content/common",
+    "//components/subresource_filter/core/common",
+    "//components/subresource_filter/core/common:test_support",
+    "//components/test_runner",
+    "//content/public/renderer",
+    "//testing/gmock",
+    "//testing/gtest",
+    "//third_party/WebKit/public:blink",
+    "//url",
   ]
 }