Move device/core files to device/base directory.

The files are being moved from device/core to device/base to follow
the de-facto standards in other directories (such as net/,
ui/, cc/, ...)

I also fixed the FOR_EACH_OBSERVER calls which are now prohibited
(git cl upload was complaining).

BUG=

Review-Url: https://codereview.chromium.org/2417043002
Cr-Commit-Position: refs/heads/master@{#425173}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 2bee1e8..bcf860a 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -1415,8 +1415,8 @@
     "//courgette:courgette_lib",
     "//crypto",
     "//crypto:platform",
+    "//device/base",
     "//device/bluetooth:mojo",
-    "//device/core",
     "//device/usb/mojo",
     "//device/usb/public/interfaces",
     "//google_apis",