device/bluetooth: Add abstract API definition for BluetoothGattDescriptor.

This CL defines the abstract class BluetoothGattDesciptor, which represents
remote and local GATT characteristic descriptors in the GATT API.

BUG=340525
TEST=Compile Chrome.

Review URL: https://codereview.chromium.org/134263008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250899 0039d316-1c4b-4281-b951-d872f2087c98
Prompt for extension install on startup even when --force-app-mode is passed

This ensures that extensions installed with --install-from-webstore still show
an install prompt.

BUG=342949
TEST=See bug for repro
NOTRY=true

Review URL: https://codereview.chromium.org/146093006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250900 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250900
Add CachingFileSystem on top of CloudStorageFileSystem
to improve performance of the docserver, avoiding hit Cloud Storage
on every request.

BUG=343315
NOTRY=true

Review URL: https://codereview.chromium.org/162043003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250901 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250901