Fixes #179 -- compile error if editing files during server mode

Fixes #179 -- compile error if editing files during server mode

this avoids reloading file contents many times during a compile. `.contents.data` == bad!
also fixes #73, using Analyzer's LineInfo instead of FileSpan to avoid finding line breaks over and over
I did some manual testing on sunflower as well as diffing SDK messages before and after

The one baseline change (23 -> 22) seems more accurate than it was before.

R=vsm@google.com

Committed: https://github.com/dart-lang/dev_compiler/commit/cad7897b28b0542c79d7f0ea935279077402fa8f

[Jennifer Messerly, 2015-05-13 23:21:15]

jmesserly@google.com changed reviewers:
+ vsm@google.com

[Jennifer Messerly, 2015-05-13 23:21:16]

https://codereview.chromium.org/1141013002/diff/1/bin/edit_files.dart
File bin/edit_files.dart (right):

https://codereview.chromium.org/1141013002/diff/1/bin/edit_files.dart#newcode79
bin/edit_files.dart:79: Source findSource(Uri uri) {
this was only used by edit_files, so moved here

https://codereview.chromium.org/1141013002/diff/1/lib/devc.dart
File lib/devc.dart (right):

https://codereview.chromium.org/1141013002/diff/1/lib/devc.dart#newcode45
lib/devc.dart:45: abstract class CompilerContext {
these 4 things get passed around together a lot

https://codereview.chromium.org/1141013002/diff/1/lib/devc.dart#newcode206
lib/devc.dart:206: bool logErrors(Source source) {
moved from "TypeResolver"

https://codereview.chromium.org/1141013002/diff/1/lib/src/checker/resolver.dart
File lib/src/checker/resolver.dart (right):

https://codereview.chromium.org/1141013002/diff/1/lib/src/checker/resolver.da...
lib/src/checker/resolver.dart:34: class TypeResolver {
happy to remove this type in follow up CL. It doesn't do anything anymore, and
the name is nonsensical. Even the file that it lives in doesn't make sense.

https://codereview.chromium.org/1141013002/diff/1/lib/src/codegen/reify_coerc...
File lib/src/codegen/reify_coercions.dart (right):

https://codereview.chromium.org/1141013002/diff/1/lib/src/codegen/reify_coerc...
lib/src/codegen/reify_coercions.dart:165: var span = utils.createSpan(_context,
_unit, begin, e.end);
this is the span that got better. Not sure why it was off by one before.

[vsm, 2015-05-14 22:02:08]

lgtm with some nits below

https://codereview.chromium.org/1141013002/diff/1/lib/devc.dart
File lib/devc.dart (right):

https://codereview.chromium.org/1141013002/diff/1/lib/devc.dart#newcode45
lib/devc.dart:45: abstract class CompilerContext {
On 2015/05/13 23:21:16, John Messerly wrote:
> these 4 things get passed around together a lot

"Context" is a bit overloaded here with CompilerContext and AnalyzerContext. 
When I see a context variable, I have to look up which type it is.  How about
"CompilerInfo" or "CompilerData" instead?  Or maybe 
"AbstractCompiler" - that matches your subsequent naming better.

https://codereview.chromium.org/1141013002/diff/1/lib/devc.dart#newcode62
lib/devc.dart:62: final List _generators = <CodeGenerator>[];
Could drop the lhs type.

https://codereview.chromium.org/1141013002/diff/1/lib/devc.dart#newcode340
lib/devc.dart:340: class AnalyzerError extends Message {
Perhaps this would fit better in info.dart where we have our other messages. 
We're already importing that here.

https://codereview.chromium.org/1141013002/diff/1/lib/src/checker/resolver.dart
File lib/src/checker/resolver.dart (right):

https://codereview.chromium.org/1141013002/diff/1/lib/src/checker/resolver.da...
lib/src/checker/resolver.dart:34: class TypeResolver {
On 2015/05/13 23:21:16, John Messerly wrote:
> happy to remove this type in follow up CL. It doesn't do anything anymore, and
> the name is nonsensical. Even the file that it lives in doesn't make sense.

sgtm

[Jennifer Messerly, 2015-05-14 23:42:21]

thanks!

https://codereview.chromium.org/1141013002/diff/1/lib/devc.dart
File lib/devc.dart (right):

https://codereview.chromium.org/1141013002/diff/1/lib/devc.dart#newcode45
lib/devc.dart:45: abstract class CompilerContext {
On 2015/05/14 22:02:08, vsm wrote:
> On 2015/05/13 23:21:16, John Messerly wrote:
> > these 4 things get passed around together a lot
> 
> "Context" is a bit overloaded here with CompilerContext and AnalyzerContext. 
> When I see a context variable, I have to look up which type it is.  How about
> "CompilerInfo" or "CompilerData" instead?  Or maybe 
> "AbstractCompiler" - that matches your subsequent naming better.

yeah, the idea was to be our equivalent of AnalysisContext. But AbstractCompiler
works for me too

https://codereview.chromium.org/1141013002/diff/1/lib/devc.dart#newcode62
lib/devc.dart:62: final List _generators = <CodeGenerator>[];
On 2015/05/14 22:02:08, vsm wrote:
> Could drop the lhs type.

Done.

https://codereview.chromium.org/1141013002/diff/1/lib/devc.dart#newcode340
lib/devc.dart:340: class AnalyzerError extends Message {
On 2015/05/14 22:02:08, vsm wrote:
> Perhaps this would fit better in info.dart where we have our other messages. 
> We're already importing that here.

good idea, done!

[Jennifer Messerly, 2015-05-14 23:42:37]

Committed patchset #3 (id:40001) manually as
cad7897b28b0542c79d7f0ea935279077402fa8f (presubmit successful).