update changelog for 1.9.3 release and date

update changelog for 1.9.3 release and date

R=nweiz@google.com

Committed: https://code.google.com/p/dart/source/detail?r=45179

[kevmoo, 2015-04-15 03:08:22]

kevmoo@google.com changed reviewers:
+ nweiz@google.com, ricow@google.com

[ricow1, 2015-04-15 05:45:52]

I think the level of detail here is a little to much. Do we expect to add
entries for all issues we resolve for 1.10?

[kevmoo, 2015-04-15 05:47:06]

On 2015/04/15 05:45:52, ricow1 wrote:
> I think the level of detail here is a little to much. Do we expect to add
> entries for all issues we resolve for 1.10?

Nope. For updates to stable channel, we want folks to know what bugs got fixed
– so they can decide if it's worth the update.

Big releases don't have this level of granularity because they generally track
bigger feature-level changes.

[nweiz, 2015-04-15 19:44:11]

lgtm

[kevmoo, 2015-04-15 19:48:00]

Committed patchset #3 (id:40001) manually as 45179 (presubmit successful).