Update COMPILATION_UNIT_CONSTANTS after incremental elements building.

pkg/analyzer/lib/src/context/context.dart

Index: pkg/analyzer/lib/src/context/context.dart
diff --git a/pkg/analyzer/lib/src/context/context.dart b/pkg/analyzer/lib/src/context/context.dart
index 858fd0636a60235d799a0f331834c973c7a6e256..4993e19fefe368dfcd0452113222a3da572cd92c 100644
--- a/pkg/analyzer/lib/src/context/context.dart
+++ b/pkg/analyzer/lib/src/context/context.dart
@@ -1864,6 +1864,15 @@ class AnalysisContextImpl implements InternalAnalysisContext {
             builder.build();
             CompilationUnitElementDelta unitDelta = builder.unitDelta;
             if (!unitDelta.hasDirectiveChange) {
+              // Update constants.
+              {
+                ConstantFinder finder =
+                    new ConstantFinder(this, source, librarySource);
+                oldUnit.accept(finder);
+                unitEntry.setValueIncremental(COMPILATION_UNIT_CONSTANTS,
+                    finder.constantsToCompute.toList(), false);
+              }
+              // Build DartDelta.
               DartDelta dartDelta = new DartDelta(source);
               dartDelta.hasDirectiveChange = unitDelta.hasDirectiveChange;
               unitDelta.addedDeclarations.forEach(dartDelta.elementChanged);