Refactor fuzzy arrow hints.

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

Index: pkg/analyzer/lib/src/dart/error/hint_codes.dart
diff --git a/pkg/analyzer/lib/src/dart/error/hint_codes.dart b/pkg/analyzer/lib/src/dart/error/hint_codes.dart
index 48de43d59a0a561da7b876a695dd451e504d1d57..63067a879b6eaff610c341ba79a01bb167b276ca 100644
--- a/pkg/analyzer/lib/src/dart/error/hint_codes.dart
+++ b/pkg/analyzer/lib/src/dart/error/hint_codes.dart
@@ -37,6 +37,18 @@ class HintCode extends ErrorCode {
       'ARGUMENT_TYPE_NOT_ASSIGNABLE',
       "The argument type '{0}' can't be assigned to the parameter type '{1}'.");
 
+  /**
+   * This hint is generated when a function type is assigned to a function
+   * typed location, and the assignment will be invalid after fuzzy arrows
+   * (the treatment of dynamic as bottom in certain locations) is removed.
+   *
+   */
+  static const HintCode USES_DYNAMIC_AS_BOTTOM = const HintCode(
+      'USES_DYNAMIC_AS_BOTTOM',
+      "A function of type '{0}' can't be assigned to a variable of type '{1}'.",
+      "Try changing the type of the function, or "
+      "casting the right-hand type to '{1}'.");
+
   /**
    * When the target expression uses '?.' operator, it can be `null`, so all the
    * subsequent invocations should also use '?.' operator.