Add support for assert statements with messages to the analyzer.

pkg/analyzer/lib/src/generated/engine.dart

Index: pkg/analyzer/lib/src/generated/engine.dart
diff --git a/pkg/analyzer/lib/src/generated/engine.dart b/pkg/analyzer/lib/src/generated/engine.dart
index 5eccbf7ee5b33c7932856815551ae5e221f02f47..68701475f5aa44f1f1344738ea0a227e18ca819d 100644
--- a/pkg/analyzer/lib/src/generated/engine.dart
+++ b/pkg/analyzer/lib/src/generated/engine.dart
@@ -1133,6 +1133,7 @@ class AnalysisContextImpl implements InternalAnalysisContext {
         (this._options.hint && !options.hint) ||
         this._options.preserveComments != options.preserveComments ||
         this._options.strongMode != options.strongMode ||
+        this._options.enableAssertMessage != options.enableAssertMessage ||
         this._options.enableStrictCallChecks !=
             options.enableStrictCallChecks ||
         this._options.enableSuperMixins != options.enableSuperMixins;
@@ -1160,6 +1161,7 @@ class AnalysisContextImpl implements InternalAnalysisContext {
     this._options.generateImplicitErrors = options.generateImplicitErrors;
     this._options.generateSdkErrors = options.generateSdkErrors;
     this._options.dart2jsHint = options.dart2jsHint;
+    this._options.enableAssertMessage = options.enableAssertMessage;
     this._options.enableStrictCallChecks = options.enableStrictCallChecks;
     this._options.enableSuperMixins = options.enableSuperMixins;
     this._options.hint = options.hint;
@@ -6202,6 +6204,11 @@ abstract class AnalysisOptions {
   bool get dart2jsHint;
 
   /**
+   * Return `true` to enable custom assert messages (DEP 37).
+   */
+  bool get enableAssertMessage;
+
+  /**
    * Return `true` if analysis is to include the new async support.
    */
   @deprecated // Always true
@@ -6335,6 +6342,12 @@ class AnalysisOptionsImpl implements AnalysisOptions {
   bool dart2jsHint = false;
 
   /**
+   * A flag indicating whether custom assert messages are to be supported (DEP
+   * 37).
+   */
+  bool enableAssertMessage = false;
+
+  /**
    * A flag indicating whether generic methods are to be supported (DEP 22).
    */
   bool enableGenericMethods = false;
@@ -6416,6 +6429,7 @@ class AnalysisOptionsImpl implements AnalysisOptions {
     analyzeFunctionBodiesPredicate = options.analyzeFunctionBodiesPredicate;
     cacheSize = options.cacheSize;
     dart2jsHint = options.dart2jsHint;
+    enableAssertMessage = options.enableAssertMessage;
     enableStrictCallChecks = options.enableStrictCallChecks;
     enableSuperMixins = options.enableSuperMixins;
     generateImplicitErrors = options.generateImplicitErrors;
@@ -6437,6 +6451,7 @@ class AnalysisOptionsImpl implements AnalysisOptions {
     analyzeFunctionBodiesPredicate = options.analyzeFunctionBodiesPredicate;
     cacheSize = options.cacheSize;
     dart2jsHint = options.dart2jsHint;
+    enableAssertMessage = options.enableAssertMessage;
     enableStrictCallChecks = options.enableStrictCallChecks;
     enableSuperMixins = options.enableSuperMixins;
     generateImplicitErrors = options.generateImplicitErrors;
@@ -8495,7 +8510,8 @@ class GenerateDartErrorsTask extends AnalysisTask {
           libraryElement,
           typeProvider,
           new InheritanceManager(libraryElement),
-          context.analysisOptions.enableSuperMixins);
+          context.analysisOptions.enableSuperMixins,
+          context.analysisOptions.enableAssertMessage);
       _unit.accept(errorVerifier);
       _errors = errorListener.getErrorsForSource(source);
     });
@@ -10947,7 +10963,8 @@ class ResolveDartUnitTask extends AnalysisTask {
           _libraryElement,
           typeProvider,
           inheritanceManager,
-          context.analysisOptions.enableSuperMixins);
+          context.analysisOptions.enableSuperMixins,
+          context.analysisOptions.enableAssertMessage);
       unit.accept(errorVerifier);
       // TODO(paulberry): as a temporary workaround for issue 21572,
       // ConstantVerifier is being run right after ConstantValueComputer, so we