Add implicit dart:core import when resynthsize from Kernel.

pkg/analyzer/lib/src/dart/element/element.dart

Index: pkg/analyzer/lib/src/dart/element/element.dart
diff --git a/pkg/analyzer/lib/src/dart/element/element.dart b/pkg/analyzer/lib/src/dart/element/element.dart
index 122de77747d5d01faa4d22802c298c7d936616dc..2f2e18798cfb06412e3f5dbb7d9b0a2254165f01 100644
--- a/pkg/analyzer/lib/src/dart/element/element.dart
+++ b/pkg/analyzer/lib/src/dart/element/element.dart
@@ -5785,6 +5785,11 @@ class ImportElementImpl extends UriReferencedElementImpl
    */
   final kernel.LibraryDependency _kernel;
 
+  /**
+   * Whether this import is synthetic.
+   */
+  final bool _kernelSynthetic;
+
   /**
    * The offset of the prefix of this import in the file that contains the this
    * import directive, or `-1` if this import is synthetic.
@@ -5821,14 +5826,17 @@ class ImportElementImpl extends UriReferencedElementImpl
       : _unlinkedImport = null,
         _linkedDependency = null,
         _kernel = null,
+        _kernelSynthetic = false,
         super(null, offset);
 
   /**
    * Initialize using the given kernel.
    */
-  ImportElementImpl.forKernel(LibraryElementImpl enclosingLibrary, this._kernel)
+  ImportElementImpl.forKernel(LibraryElementImpl enclosingLibrary, this._kernel,
+      {bool isSynthetic: false})
       : _unlinkedImport = null,
         _linkedDependency = null,
+        _kernelSynthetic = isSynthetic,
         super.forSerialized(enclosingLibrary);
 
   /**
@@ -5837,6 +5845,7 @@ class ImportElementImpl extends UriReferencedElementImpl
   ImportElementImpl.forSerialized(this._unlinkedImport, this._linkedDependency,
       LibraryElementImpl enclosingLibrary)
       : _kernel = null,
+        _kernelSynthetic = false,
         super.forSerialized(enclosingLibrary);
 
   @override
@@ -5907,6 +5916,9 @@ class ImportElementImpl extends UriReferencedElementImpl
 
   @override
   bool get isSynthetic {
+    if (_kernel != null) {
+      return _kernelSynthetic;
+    }
     if (_unlinkedImport != null) {
       return _unlinkedImport.isImplicit;
     }
@@ -6083,6 +6095,14 @@ class ImportElementImpl extends UriReferencedElementImpl
  * The kernel context in which a library is resynthesized.
  */
 abstract class KernelLibraryResynthesizerContext {
+  /**
+   * The Kernel library for `dart:core`.
+   */
+  kernel.Library get coreLibrary;
+
+  /**
+   * The Kernel library being resynthesized.
+   */
   kernel.Library get library;
 
   /**
@@ -6234,6 +6254,8 @@ class LabelElementImpl extends ElementImpl implements LabelElement {
  * A concrete implementation of a [LibraryElement].
  */
 class LibraryElementImpl extends ElementImpl implements LibraryElement {
+  static final Uri _dartCore = Uri.parse('dart:core');
+
   /**
    * The analysis context in which this library is defined.
    */
@@ -6547,10 +6569,36 @@ class LibraryElementImpl extends ElementImpl implements LibraryElement {
   List<ImportElement> get imports {
     if (_imports == null) {
       if (_kernelContext != null) {
-        _imports = _kernelContext.library.dependencies
-            .where((k) => k.isImport)
-            .map((k) => new ImportElementImpl.forKernel(this, k))
-            .toList(growable: false);
+        var dependencies = _kernelContext.library.dependencies;
+        int numOfDependencies = dependencies.length;
+        // Compute the number of import dependencies.
+        bool hasCore = false;
+        int numOfImports = 0;
+        for (int i = 0; i < numOfDependencies; i++) {
+          kernel.LibraryDependency dependency = dependencies[i];
+          if (dependency.isImport) {
+            numOfImports++;
+            if (dependency.targetLibrary.importUri == _dartCore) {
+              hasCore = true;
+            }
+          }
+        }
+        // Create import elements.
+        var imports = new List<ImportElement>(numOfImports + (hasCore ? 0 : 1));
+        for (int i = 0; i < numOfDependencies; i++) {
+          kernel.LibraryDependency dependency = dependencies[i];
+          if (dependency.isImport) {
+            imports[i] = new ImportElementImpl.forKernel(this, dependency);
+          }
+        }
+        // If dart:core is not imported explicitly, import it implicitly.
+        if (!hasCore) {
+          imports[numOfImports] = new ImportElementImpl.forKernel(this,
+              new kernel.LibraryDependency.import(_kernelContext.coreLibrary),
+              isSynthetic: true);
+        }
+        // Set imports into the field.
+        _imports = imports;
       }
       if (_unlinkedDefiningUnit != null) {
         List<UnlinkedImport> unlinkedImports = _unlinkedDefiningUnit.imports;