Move more of webcore_remaining into GN build files.

third_party/WebKit/Source/core/fileapi/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("fileapi") {
+  sources = [
+    "Blob.cpp",
+    "Blob.h",
+    "BlobCallback.h",
+    "File.cpp",
+    "File.h",
+    "FileError.cpp",
+    "FileError.h",
+    "FileList.cpp",
+    "FileList.h",
+    "FileReader.cpp",
+    "FileReader.h",
+    "FileReaderLoader.cpp",
+    "FileReaderLoader.h",
+    "FileReaderLoaderClient.h",
+    "FileReaderSync.cpp",
+    "FileReaderSync.h",
+    "URLFileAPI.cpp",
+    "URLFileAPI.h",
+  ]
+
+  configs += [
+    # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
+    "//build/config/compiler:no_size_t_to_int_warning",
+  ]
+}