Break ConsentProvider classes into own file

file_system_api.cc/h is large and has lots of dependencies. Split out
the Chrome OS UI-specific helper classes, ConsentProvider and
ConsentProviderDelegate, into consent_provider.cc/h.

Also moves the ConsentProvider unit tests into its own file.

BUG=729713

Review-Url: https://codereview.chromium.org/2924943003
Cr-Commit-Position: refs/heads/master@{#478337}
diff --git a/chrome/browser/extensions/BUILD.gn b/chrome/browser/extensions/BUILD.gn
index 1764a87..1c21a59c 100644
--- a/chrome/browser/extensions/BUILD.gn
+++ b/chrome/browser/extensions/BUILD.gn
@@ -935,6 +935,8 @@
       "api/enterprise_platform_keys/enterprise_platform_keys_api.h",
       "api/enterprise_platform_keys_private/enterprise_platform_keys_private_api.cc",
       "api/enterprise_platform_keys_private/enterprise_platform_keys_private_api.h",
+      "api/file_system/consent_provider.cc",
+      "api/file_system/consent_provider.h",
       "api/file_system/request_file_system_notification.cc",
       "api/file_system/request_file_system_notification.h",
       "api/input_ime/input_ime_api.cc",