Add a message to the IllegalArgumentException thrown when a

DateValue/DateTimeValue/TimeOfDayValue is created with a GregorianCalendar that
is not GMT.

Author: shubay

src/main/java/com/google/visualization/datasource/datatable/value/DateTimeValue.java

@@ -123,7 +123,8 @@ public DateTimeValue(int year, int month, int dayOfMonth, int hours,
    */
   public DateTimeValue(GregorianCalendar calendar) {
     if (!calendar.getTimeZone().equals(TimeZone.getTimeZone("GMT"))) {
-      throw new IllegalArgumentException();
+      throw new IllegalArgumentException(
+          "Can't create DateTimeValue from GregorianCalendar that is not GMT.");
     }
     this.calendar = (GregorianCalendar) calendar.clone();
   }

src/main/java/com/google/visualization/datasource/datatable/value/DateValue.java

@@ -124,7 +124,8 @@ public DateValue(int year, int month, int dayOfMonth) {
    */
   public DateValue(GregorianCalendar calendar) {
     if (!calendar.getTimeZone().equals(TimeZone.getTimeZone("GMT"))) {
-      throw new IllegalArgumentException();
+      throw new IllegalArgumentException(
+           "Can't create DateValue from GregorianCalendar that is not GMT.");
     }
     this.year = calendar.get(GregorianCalendar.YEAR);
     this.month = calendar.get(GregorianCalendar.MONTH);

src/main/java/com/google/visualization/datasource/datatable/value/TimeOfDayValue.java

@@ -143,7 +143,8 @@ public TimeOfDayValue(int hours, int minutes, int seconds, int milliseconds) {
    */
   public TimeOfDayValue(GregorianCalendar calendar) {
     if (!calendar.getTimeZone().equals(TimeZone.getTimeZone("GMT"))) {
-      throw new IllegalArgumentException();
+      throw new IllegalArgumentException(
+          "Can't create TimeOfDayValue from GregorianCalendar that is not GMT.");
     }
     this.hours = calendar.get(GregorianCalendar.HOUR_OF_DAY);
     this.minutes = calendar.get(GregorianCalendar.MINUTE);