Add CdmFileIOProvider interface for use by cdm_adapter

media/BUILD.gn

Index: media/BUILD.gn
diff --git a/media/BUILD.gn b/media/BUILD.gn
index d738e2c4d361375d531467c5f8c7b2bd6926d601..dbc57d674191cc29b39126ef584ace66735a1f84 100644
--- a/media/BUILD.gn
+++ b/media/BUILD.gn
@@ -78,6 +78,8 @@ component("media") {
     "cdm/cdm_adapter.h",
     "cdm/cdm_allocator.cc",
     "cdm/cdm_allocator.h",
+    "cdm/cdm_file_io_provider.cc",
+    "cdm/cdm_file_io_provider.h",
     "cdm/cdm_helpers.cc",
     "cdm/cdm_helpers.h",
     "cdm/default_cdm_factory.cc",
@@ -496,6 +498,8 @@ test("media_unittests") {
     "cdm/simple_cdm_allocator_unittest.cc",
     "cdm/simple_cdm_buffer.cc",
     "cdm/simple_cdm_buffer.h",
+    "cdm/simple_cdm_file_io_provider.cc",
+    "cdm/simple_cdm_file_io_provider.h",
     "filters/audio_clock_unittest.cc",
     "filters/audio_decoder_selector_unittest.cc",
     "filters/audio_renderer_algorithm_unittest.cc",