Improve the error message when DateTime parsing fails verification.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=150657659

Author: alan-knight

CHANGELOG.md

@@ -13,6 +13,8 @@
    UninitializedLocaleData.throwOnFallback.
  * Restore dependency on path which was removed when intl_translation was
    separated.
+ * Improve the error message when date parsing fails validation to show what the
+   parsed date was.
 
 ## 0.14.0
  * MAJOR BREAKING CHANGE! Remove message extraction and code generation into a

lib/src/intl/date_format_helpers.dart

@@ -66,16 +66,18 @@ class _DateBuilder {
     // check the year, which we otherwise can't verify, and the hours,
     // which will catch cases like "14:00:00 PM".
     var date = asDate();
-    _verify(hour24, date.hour, date.hour, "hour", s);
-    _verify(day, date.day, date.day, "day", s);
-    _verify(year, date.year, date.year, "year", s);
+    _verify(hour24, date.hour, date.hour, "hour", s, date);
+    _verify(day, date.day, date.day, "day", s, date);
+    _verify(year, date.year, date.year, "year", s, date);
   }
 
-  _verify(int value, int min, int max, String desc, String originalInput) {
+  _verify(int value, int min, int max, String desc, String originalInput,
+      [DateTime parsed]) {
     if (value < min || value > max) {
+      var parsedDescription = parsed == null ? "" : " Date parsed as $parsed.";
       throw new FormatException(
           "Error parsing $originalInput, invalid $desc value: $value."
-          " Expected value between $min and $max.");
+          " Expected value between $min and $max.$parsedDescription");
     }
   }