Add static type checking of "yield" statements to analyzer.

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

Index: pkg/analyzer/lib/src/generated/error.dart
diff --git a/pkg/analyzer/lib/src/generated/error.dart b/pkg/analyzer/lib/src/generated/error.dart
index f9411ef8fa5028af35cc29fee855e5d307e3517a..e5faa78996adcbd367efa2bd98c284b204a6b5f5 100644
--- a/pkg/analyzer/lib/src/generated/error.dart
+++ b/pkg/analyzer/lib/src/generated/error.dart
@@ -3716,6 +3716,22 @@ class StaticTypeWarningCode extends ErrorCode {
           "The type '{0}' is declared with {1} type parameters, but {2} type arguments were given");
 
   /**
+   * 17.16.1 Yield: Let T be the static type of e [the expression to the right
+   * of "yield"] and let f be the immediately enclosing function.  It is a
+   * static type warning if either:
+   *
+   * - the body of f is marked async* and the type Stream<T> may not be
+   *   assigned to the declared return type of f.
+   *
+   * - the body of f is marked sync* and the type Iterable<T> may not be
+   *   assigned to the declared return type of f.
+   */
+  static const StaticTypeWarningCode YIELD_OF_INVALID_TYPE =
+      const StaticTypeWarningCode(
+          'YIELD_OF_INVALID_TYPE',
+          "The declared return type '{0}' is incompatible with the type '{1}' implied by the 'yield' expression");
+
+  /**
    * Initialize a newly created error code to have the given [name]. The message
    * associated with the error will be created from the given [message]
    * template. The correction associated with the error will be created from the