Add import dependencies to Kernel libraries and use them to resynthesize ImportElement(s) in Analyz…

pkg/kernel/lib/text/ast_to_text.dart

Index: pkg/kernel/lib/text/ast_to_text.dart
diff --git a/pkg/kernel/lib/text/ast_to_text.dart b/pkg/kernel/lib/text/ast_to_text.dart
index b3f976c4210fc1cbb02315606ddc77dfbac2ad04..f5151efc71377b71d4c6fac22894273c14403854 100644
--- a/pkg/kernel/lib/text/ast_to_text.dart
+++ b/pkg/kernel/lib/text/ast_to_text.dart
@@ -283,12 +283,8 @@ class Printer extends Visitor<Null> {
         endLine('import "$importPath" as $prefix;');
       }
     }
-    for (var import in library.dependencies) {

[Siggi Cherem (dart-lang), 2017/07/20 18:29:00]

I'm not sure I understand this part of the change. This means we no longer print
out library dependencies? Is this to avoid changes to the expectation files in
our unit tests?

If so, I would prefer not to make this change here, but update the expectations
or make a change that doesn't affect regular printing but affects printing of
external libraries only?

[scheglov, 2017/07/20 19:33:53]

First of all, this code has not been used, because we used not to add
dependencies to libraries when building them. Instead, the code about uses
LibraryImportTable to gather "actually used" imports and generate synthetic
prefixes assigned to them, and then we print only these "actually used" imports
into text presentation.

I agree that if we want to have our tests validate that we add required
import/export dependencies into kernels as we build them, we need to update all
the expectations. One nasty consequence of this would be that we will have
duplicate sets of imports - one for "actually used" and another for "specified".
If that's what you think is OK, then I can update all expectations.

[Siggi Cherem (dart-lang), 2017/07/20 22:50:36]

Thanks so much for the clarification. Given your explanation, I'm OK submitting
this change as it is. Let's write a TODO and open a bug to follow up with the
kernel-team on this issue. It seems low priority, but they can let us know if
they have any concerns.

[scheglov, 2017/07/21 16:21:33]

I will add TODO, https://github.com/dart-lang/sdk/issues/30224

-      import.accept(this);
-    }
     endLine();
     var inner = new Printer._inner(this, imports);
-    library.dependencies.forEach(inner.writeNode);
     library.typedefs.forEach(inner.writeNode);
     library.classes.forEach(inner.writeNode);
     library.fields.forEach(inner.writeNode);