Avoid extra delays in the code completion.

1. Remove 80 ms delay before requesting code completion.

2. Cache focus / caret offset in UI thread.
   Switching to UI thread is expensive - it might cost 150 ms each.
   So, we save about 200-300 ms here.

R=danrubel@google.com
BUG=

Review URL: https://codereview.chromium.org//792243003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42293 260f80e4-7a28-3924-810f-c04153c831b5
Redo "Make StringBuffer.write easier to inline"

Verified passes on Safari Version 7.1 (9537.85.10.17.1)

TBR=floitsch@google.com

Review URL: https://codereview.chromium.org//797733002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42294 260f80e4-7a28-3924-810f-c04153c831b5
Don't refresh the Outline page when input hasn't really changed.

This helps us to save 50-70 ms before displaying completion items.

R=brianwilkerson@google.com
BUG=

Review URL: https://codereview.chromium.org//798553003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42295 260f80e4-7a28-3924-810f-c04153c831b5