Revert "Use native async/await support in pub."

sdk/lib/_internal/pub_generated/lib/src/solver/backtracking_solver.dart

Index: sdk/lib/_internal/pub_generated/lib/src/solver/backtracking_solver.dart
diff --git a/sdk/lib/_internal/pub/lib/src/solver/backtracking_solver.dart b/sdk/lib/_internal/pub_generated/lib/src/solver/backtracking_solver.dart
similarity index 93%
copy from sdk/lib/_internal/pub/lib/src/solver/backtracking_solver.dart
copy to sdk/lib/_internal/pub_generated/lib/src/solver/backtracking_solver.dart
index a9b84e37184be33f42ba2b6ab18c6a423324693d..a5bac0f8ef66d369a5b2da8cee7d8dad908acbc5 100644
--- a/sdk/lib/_internal/pub/lib/src/solver/backtracking_solver.dart
+++ b/sdk/lib/_internal/pub_generated/lib/src/solver/backtracking_solver.dart
@@ -109,7 +109,7 @@ class BacktrackingSolver {
   var _attemptedSolutions = 1;
 
   BacktrackingSolver(SolveType type, SourceRegistry sources, this.root,
-          this.lockFile, List<String> useLatest)
+      this.lockFile, List<String> useLatest)
       : type = type,
         sources = sources,
         cache = new PubspecCache(type, sources) {
@@ -146,22 +146,33 @@ class BacktrackingSolver {
       _validateSdkConstraint(root.pubspec);
       return _traverseSolution();
     }).then((packages) {
-      var pubspecs = new Map.fromIterable(packages,
+      var pubspecs = new Map.fromIterable(
+          packages,
           key: (id) => id.name,
           value: (id) => cache.getCachedPubspec(id));
 
       return Future.wait(
-              packages.map((id) => sources[id.source].resolveId(id)))
-          .then((packages) {
-        return new SolveResult.success(sources, root, lockFile, packages,
-            overrides, pubspecs, _getAvailableVersions(packages),
+          packages.map((id) => sources[id.source].resolveId(id))).then((packages) {
+        return new SolveResult.success(
+            sources,
+            root,
+            lockFile,
+            packages,
+            overrides,
+            pubspecs,
+            _getAvailableVersions(packages),
             attemptedSolutions);
       });
     }).catchError((error) {
       if (error is! SolveFailure) throw error;
       // Wrap a failure in a result so we can attach some other data.
-      return new SolveResult.failure(sources, root, lockFile, overrides,
-          error, attemptedSolutions);
+      return new SolveResult.failure(
+          sources,
+          root,
+          lockFile,
+          overrides,
+          error,
+          attemptedSolutions);
     }).whenComplete(() {
       // Gather some solving metrics.
       var buffer = new StringBuffer();
@@ -527,7 +538,8 @@ class Traverser {
       // Make sure the package doesn't have any bad dependencies.
       for (var dep in deps) {
         if (!dep.isRoot && _solver.sources[dep.source] is UnknownSource) {
-          throw new UnknownSourceException(id.name,
+          throw new UnknownSourceException(
+              id.name,
               [new Dependency(id.name, id.version, dep)]);
         }
       }
@@ -576,11 +588,9 @@ class Traverser {
 
       // See if it's possible for a package to match that constraint.
       if (constraint.isEmpty) {
-        var constraints = dependencies
-            .map((dep) => "  ${dep.dep.constraint} from ${dep.depender}")
-            .join('\n');
-        _solver.logSolve(
-            'disjoint constraints on ${dep.name}:\n$constraints');
+        var constraints = dependencies.map(
+            (dep) => "  ${dep.dep.constraint} from ${dep.depender}").join('\n');
+        _solver.logSolve('disjoint constraints on ${dep.name}:\n$constraints');
         throw new DisjointConstraintException(dep.name, dependencies);
       }
 
@@ -611,7 +621,10 @@ class Traverser {
 
       if (allowed.isEmpty) {
         _solver.logSolve('no versions for ${dep.name} match $constraint');
-        throw new NoVersionException(dep.name, null, constraint,
+        throw new NoVersionException(
+            dep.name,
+            null,
+            constraint,
             _getDependencies(dep.name));
       }
 
@@ -630,7 +643,9 @@ class Traverser {
       if (error is PackageNotFoundException) {
         // Show the user why the package was being requested.
         throw new DependencyNotFoundException(
-            dep.name, error, _getDependencies(dep.name));
+            dep.name,
+            error,
+            _getDependencies(dep.name));
       }
 
       throw error;
@@ -651,16 +666,17 @@ class Traverser {
 
     // Make sure all of the existing sources match the new reference.
     if (required.dep.source != dep.source) {
-      _solver.logSolve('source mismatch on ${dep.name}: ${required.dep.source} '
-                       '!= ${dep.source}');
+      _solver.logSolve(
+          'source mismatch on ${dep.name}: ${required.dep.source} ' '!= ${dep.source}');
       throw new SourceMismatchException(dep.name, [required, dependency]);
     }
 
     // Make sure all of the existing descriptions match the new reference.
     var source = _solver.sources[dep.source];
     if (!source.descriptionsEqual(dep.description, required.dep.description)) {
-      _solver.logSolve('description mismatch on ${dep.name}: '
-                       '${required.dep.description} != ${dep.description}');
+      _solver.logSolve(
+          'description mismatch on ${dep.name}: '
+              '${required.dep.description} != ${dep.description}');
       throw new DescriptionMismatchException(dep.name, [required, dependency]);
     }
   }
@@ -678,8 +694,11 @@ class Traverser {
     // Make sure it meets the constraint.
     if (!dep.constraint.allows(selected.version)) {
       _solver.logSolve('selection $selected does not match $constraint');
-      throw new NoVersionException(dep.name, selected.version, constraint,
-                                   _getDependencies(dep.name));
+      throw new NoVersionException(
+          dep.name,
+          selected.version,
+          constraint,
+          _getDependencies(dep.name));
     }
 
     return selected;
@@ -695,8 +714,8 @@ class Traverser {
 
     return Future.wait(barback.pubConstraints.keys.map((depName) {
       var constraint = barback.pubConstraints[depName];
-      _solver.logSolve('add implicit $constraint pub dependency on '
-          '$depName');
+      _solver.logSolve(
+          'add implicit $constraint pub dependency on ' '$depName');
 
       var override = _solver._overrides[depName];
 
@@ -731,16 +750,17 @@ class Traverser {
   /// can have a bunch of dependencies back onto the root package as long as
   /// they all agree with each other.
   Dependency _getRequired(String name) {
-    return _getDependencies(name)
-        .firstWhere((dep) => !dep.dep.isRoot, orElse: () => null);
+    return _getDependencies(
+        name).firstWhere((dep) => !dep.dep.isRoot, orElse: () => null);
   }
 
   /// Gets the combined [VersionConstraint] currently being placed on package
   /// [name].
   VersionConstraint _getConstraint(String name) {
-    var constraint = _getDependencies(name)
-        .map((dep) => dep.dep.constraint)
-        .fold(VersionConstraint.any, (a, b) => a.intersect(b));
+    var constraint = _getDependencies(
+        name).map(
+            (dep) =>
+                dep.dep.constraint).fold(VersionConstraint.any, (a, b) => a.intersect(b));
 
     return constraint;
   }
@@ -768,7 +788,8 @@ class Traverser {
 
       var source = _solver.sources[package.source];
       if (!source.descriptionsEqual(
-          package.description, required.dep.description)) return null;
+          package.description,
+          required.dep.description)) return null;
     }
 
     return package;
@@ -782,8 +803,8 @@ class Traverser {
 void _validateSdkConstraint(Pubspec pubspec) {
   if (pubspec.environment.sdkVersion.allows(sdk.version)) return;
 
-  throw new BadSdkVersionException(pubspec.name,
+  throw new BadSdkVersionException(
+      pubspec.name,
       'Package ${pubspec.name} requires SDK version '
-      '${pubspec.environment.sdkVersion} but the current SDK is '
-      '${sdk.version}.');
+          '${pubspec.environment.sdkVersion} but the current SDK is ' '${sdk.version}.');
 }