Add AnalysisDriver.getUnitElementSignature() for checking without resynthesizing.

Add AnalysisDriver.getUnitElementSignature() for checking without resynthesizing.

Just like _computeAnalysisResult() uses _getResolvedUnitKey() to check
cache for existing results without _createLibraryContext(), we need
Angular plugin to use getUnitElementSignature() to check whether there
are existing analysis results.

R=brianwilkerson@google.com
BUG=

Committed: https://github.com/dart-lang/sdk/commit/126b10adf8644e5fc4ce9655542bf043f6e59ffd

[Brian Wilkerson, 2017-02-13 20:29:10]

lgtm

[scheglov, 2017-02-13 20:45:20]

Description was changed from

==========
Add AnalysisDriver.getUnitElementSignature() for checking without
resynthesizing.

Just like _computeAnalysisResult() uses _getResolvedUnitKey() to check
cache for existing results without _createLibraryContext(), we need
Angular plugin to use getUnitElementSignature() to check whether there
are existing analysis results.

R=brianwilkerson@google.com
BUG=
==========

to

==========
Add AnalysisDriver.getUnitElementSignature() for checking without
resynthesizing.

Just like _computeAnalysisResult() uses _getResolvedUnitKey() to check
cache for existing results without _createLibraryContext(), we need
Angular plugin to use getUnitElementSignature() to check whether there
are existing analysis results.

R=brianwilkerson@google.com
BUG=

Committed:
https://github.com/dart-lang/sdk/commit/126b10adf8644e5fc4ce9655542bf043f6e59ffd
==========

[scheglov, 2017-02-13 20:45:21]

Committed patchset #1 (id:1) manually as
126b10adf8644e5fc4ce9655542bf043f6e59ffd (presubmit successful).