Fix the following browser_tests in the Linux GN build.

third_party/protobuf/BUILD.gn

Index: third_party/protobuf/BUILD.gn
diff --git a/third_party/protobuf/BUILD.gn b/third_party/protobuf/BUILD.gn
index 7c036ee5ecfc04c1b772c841ace5f0f0765bd853..215751359e75577318e39f1cf68d46f5c387ffe5 100644
--- a/third_party/protobuf/BUILD.gn
+++ b/third_party/protobuf/BUILD.gn
@@ -263,4 +263,69 @@ if (current_toolchain == host_toolchain) {
     ]
     deps += [ "//build/config/sanitizers:deps" ]
   }
+
+  copy("copy_google") {
+    sources = [
+      "__init__.py",
+    ]
+    outputs = [
+      "$root_gen_dir/google/{{source_file_part}}",
+    ]
+  }
+
+  copy("copy_google_protobuf") {
+    sources = [
+      "python/google/protobuf/__init__.py",
+      "python/google/protobuf/descriptor.py",
+      "python/google/protobuf/descriptor_database.py",
+      "python/google/protobuf/descriptor_pool.py",
+      "python/google/protobuf/message.py",
+      "python/google/protobuf/message_factory.py",
+      "python/google/protobuf/reflection.py",
+      "python/google/protobuf/service.py",
+      "python/google/protobuf/service_reflection.py",
+      "python/google/protobuf/text_format.py",
+
+      # TODO(ncarter): protoc"s python generator treats
+      # descriptor.proto specially, but it's not possible to trigger
+      # the special treatment unless you run protoc from ./src/src
+      # (the treatment is based on the path to the .proto file
+      # matching a constant exactly). I'm not sure how to convince
+      # gyp to execute a rule from a different directory.  Until this
+      # is resolved, use a copy of descriptor_pb2.py that I manually
+      # generated.
+      "descriptor_pb2.py",
+    ]
+    outputs = [
+      "$root_gen_dir/google/protobuf/{{source_file_part}}",
+    ]
+  }
+
+  copy("copy_google_protobuf_internal") {
+    sources = [
+      "python/google/protobuf/internal/__init__.py",
+      "python/google/protobuf/internal/api_implementation.py",
+      "python/google/protobuf/internal/containers.py",
+      "python/google/protobuf/internal/cpp_message.py",
+      "python/google/protobuf/internal/decoder.py",
+      "python/google/protobuf/internal/encoder.py",
+      "python/google/protobuf/internal/enum_type_wrapper.py",
+      "python/google/protobuf/internal/generator_test.py",
+      "python/google/protobuf/internal/message_listener.py",
+      "python/google/protobuf/internal/python_message.py",
+      "python/google/protobuf/internal/type_checkers.py",
+      "python/google/protobuf/internal/wire_format.py",
+    ]
+    outputs = [
+      "$root_gen_dir/google/protobuf/internal/{{source_file_part}}",
+    ]
+  }
+
+  group("py_proto") {
+    public_deps = [
+      ":copy_google",
+      ":copy_google_protobuf",
+      ":copy_google_protobuf_internal",
+    ]
+  }
 }