filter auto proposals and code for tracking completion performance

BUG=dartbug.com/21563
R=scheglov@google.com

Review URL: https://codereview.chromium.org//794053002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42288 260f80e4-7a28-3924-810f-c04153c831b5
filter imported element suggestions to reduce number of results sent to client

BUG=
R=paulberry@google.com

Review URL: https://codereview.chromium.org//795633004

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42289 260f80e4-7a28-3924-810f-c04153c831b5
Change GetAssistsConsumer to have the additional method onError.

R=brianwilkerson@google.com

Review URL: https://codereview.chromium.org//797703002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42290 260f80e4-7a28-3924-810f-c04153c831b5
Build fix- Change QuickAssistProcessor to implement additional method

Review URL: https://codereview.chromium.org//795053005

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42291 260f80e4-7a28-3924-810f-c04153c831b5
Simplify subscriptions updating implementation.

R=keertip@google.com
BUG=

Review URL: https://codereview.chromium.org//788213002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42292 260f80e4-7a28-3924-810f-c04153c831b5