Remove BrowserThread dependency from usb_service.

Instead of explicitly depending on specific browser threads the USB
service can assume that it is instantiated on BrowserThread::FILE (or
equivalent) and save a TaskRunner reference from this instantiation for
later use when called from other threads.

To reach BrowserThread::UI (required for DBus on Chrome OS) a reference
to the appropriate TaskRunner must be provided when calling
UsbService::GetInstance().

BUG=

Review URL: https://codereview.chromium.org/507503002

Cr-Commit-Position: refs/heads/master@{#292546}
diff --git a/chrome/browser/DEPS b/chrome/browser/DEPS
index d8d9246..0b17801c 100644
--- a/chrome/browser/DEPS
+++ b/chrome/browser/DEPS
@@ -70,6 +70,7 @@
   "+components/translate/core/browser",
   "+components/translate/core/common",
   "+components/url_matcher",
+  "+components/usb_service",
   "+components/user_manager",
   "+components/user_prefs",
   "+components/web_modal",
@@ -78,6 +79,7 @@
   "+content/test/net",
   "+courgette",
   "+device/bluetooth",
+  "+device/core",
   "+device/media_transfer_protocol",
   "+extensions/browser",
   "+extensions/common",