Implement Physical Web listener registration

components/physical_web/data_source/BUILD.gn

Index: components/physical_web/data_source/BUILD.gn
diff --git a/components/physical_web/data_source/BUILD.gn b/components/physical_web/data_source/BUILD.gn
index 70f92ff8c3092f5b95a86c9fe4ab91d776838d1a..4236cf08bd4e961cd44f2ca98f2acc7885796ff7 100644
--- a/components/physical_web/data_source/BUILD.gn
+++ b/components/physical_web/data_source/BUILD.gn
@@ -5,6 +5,8 @@
 source_set("data_source") {
   sources = [
     "physical_web_data_source.h",
+    "physical_web_data_source_impl.cc",
+    "physical_web_data_source_impl.h",
     "physical_web_listener.h",
   ]
 
@@ -12,3 +14,16 @@ source_set("data_source") {
     "//base",
   ]
 }
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "physical_web_data_source_impl_unittest.cc",
+  ]
+
+  deps = [
+    ":data_source",
+    "//base",
+    "//testing/gtest",
+  ]
+}