Fix analyzer's handling of import prefixes not followed by '.'.

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 03befb389fa62439eea2193059e6ea1a7fd02170..3ff91a83528543a73c64022ca2593aab057337df 100644
--- a/pkg/analyzer/lib/src/generated/error.dart
+++ b/pkg/analyzer/lib/src/generated/error.dart
@@ -1949,6 +1949,14 @@ class CompileTimeErrorCode extends ErrorCode {
           "The name '{0}' is already used as an import prefix and cannot be used to name a top-level element");
 
   /**
+   * 16.32 Identifier Reference: If d is a prefix p, a compile-time error
+   * occurs unless the token immediately following d is '.'.
+   */
+  static const CompileTimeErrorCode PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT =
+      const CompileTimeErrorCode('PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT',
+          "The name '{0}' refers to an import prefix, so it must be followed by '.'");
+
+  /**
    * 6.2.2 Optional Formals: It is a compile-time error if the name of a named
    * optional parameter begins with an '_' character.
    */