Support conditional directives in the options file.

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 cc1d41e3f9acc5b3b378dab14d5c1d5dfd9d2e08..e3ba96b8c62617f9ce87dce6ab67b0ebf1d84d35 100644
--- a/pkg/analyzer/lib/src/context/context.dart
+++ b/pkg/analyzer/lib/src/context/context.dart
@@ -260,6 +260,8 @@ class AnalysisContextImpl implements InternalAnalysisContext {
             options.enableStrictCallChecks ||
         this._options.enableGenericMethods != options.enableGenericMethods ||
         this._options.enableAsync != options.enableAsync ||
+        this._options.enableConditionalDirectives !=
+            options.enableConditionalDirectives ||
         this._options.enableSuperMixins != options.enableSuperMixins;
     int cacheSize = options.cacheSize;
     if (this._options.cacheSize != cacheSize) {
@@ -274,6 +276,8 @@ class AnalysisContextImpl implements InternalAnalysisContext {
     this._options.enableAssertMessage = options.enableAssertMessage;
     this._options.enableStrictCallChecks = options.enableStrictCallChecks;
     this._options.enableAsync = options.enableAsync;
+    this._options.enableConditionalDirectives =
+        options.enableConditionalDirectives;
     this._options.enableSuperMixins = options.enableSuperMixins;
     this._options.hint = options.hint;
     this._options.incremental = options.incremental;