Reanalyze after creating a referenced part.

pkg/analyzer/lib/src/task/dart.dart

Index: pkg/analyzer/lib/src/task/dart.dart
diff --git a/pkg/analyzer/lib/src/task/dart.dart b/pkg/analyzer/lib/src/task/dart.dart
index 9aaa8c8c98be79290fedfa40184139109bdc7b5f..f27614d91973641bd416bb10ff3df3e28df28144 100644
--- a/pkg/analyzer/lib/src/task/dart.dart
+++ b/pkg/analyzer/lib/src/task/dart.dart
@@ -1331,7 +1331,7 @@ class BuildLibraryElementTask extends SourceBasedAnalysisTask {
         Source partSource = partDirective.source;
         hasPartDirective = true;
         CompilationUnit partUnit = partUnitMap[partSource];
-        if (partUnit != null && context.exists(partSource)) {
+        if (partUnit != null) {
           CompilationUnitElementImpl partElement = partUnit.element;
           partElement.uriOffset = partUri.offset;
           partElement.uriEnd = partUri.end;
@@ -1340,24 +1340,26 @@ class BuildLibraryElementTask extends SourceBasedAnalysisTask {
           // Validate that the part contains a part-of directive with the same
           // name as the library.
           //
-          String partLibraryName =
-              _getPartLibraryName(partSource, partUnit, directivesToResolve);
-          if (partLibraryName == null) {
-            errors.add(new AnalysisError(librarySource, partUri.offset,
-                partUri.length, CompileTimeErrorCode.PART_OF_NON_PART,
-                [partUri.toSource()]));
-          } else if (libraryNameNode == null) {
-            if (partsLibraryName == _UNKNOWN_LIBRARY_NAME) {
-              partsLibraryName = partLibraryName;
-            } else if (partsLibraryName != partLibraryName) {
-              partsLibraryName = null;
+          if (context.exists(partSource)) {
+            String partLibraryName =
+                _getPartLibraryName(partSource, partUnit, directivesToResolve);
+            if (partLibraryName == null) {
+              errors.add(new AnalysisError(librarySource, partUri.offset,
+                  partUri.length, CompileTimeErrorCode.PART_OF_NON_PART,
+                  [partUri.toSource()]));
+            } else if (libraryNameNode == null) {
+              if (partsLibraryName == _UNKNOWN_LIBRARY_NAME) {
+                partsLibraryName = partLibraryName;
+              } else if (partsLibraryName != partLibraryName) {
+                partsLibraryName = null;
+              }
+            } else if (libraryNameNode.name != partLibraryName) {
+              errors.add(new AnalysisError(librarySource, partUri.offset,
+                  partUri.length, StaticWarningCode.PART_OF_DIFFERENT_LIBRARY, [
+                libraryNameNode.name,
+                partLibraryName
+              ]));
             }
-          } else if (libraryNameNode.name != partLibraryName) {
-            errors.add(new AnalysisError(librarySource, partUri.offset,
-                partUri.length, StaticWarningCode.PART_OF_DIFFERENT_LIBRARY, [
-              libraryNameNode.name,
-              partLibraryName
-            ]));
           }
           if (entryPoint == null) {
             entryPoint = _findEntryPoint(partElement);