clear mIsUtc when a non-null non-utc timezone is assigned, r=pav

calendar/base/public/calIDateTime.idl

@@ -90,7 +90,8 @@ interface calIDateTime : nsISupports
 
   // an associated timezone that's the preferred way of representing
   // this object.  If this is null/empty, then there is no preferred
-  // timezone, and UTC or localtime is assumed (based on isUtc).
+  // timezone, and UTC or localtime is assumed (based on isUtc).  If
+  // this is non-null when assigned, isUtc is automatically cleared.
   attribute AUTF8String timezone;
 
   // the offset in minutes from UTC that this date is stored in.

calendar/base/src/calDateTime.cpp

@@ -162,7 +162,23 @@ CAL_VALUETYPE_ATTR(calDateTime, PRInt32, TimezoneOffset)
 CAL_VALUETYPE_ATTR_GETTER(calDateTime, PRInt16, Weekday)
 CAL_VALUETYPE_ATTR_GETTER(calDateTime, PRInt16, Yearday)
 
-CAL_STRINGTYPE_ATTR(calDateTime, nsACString, Timezone)
+CAL_STRINGTYPE_ATTR_GETTER(calDateTime, nsACString, Timezone)
+
+NS_IMETHODIMP
+calDateTime::SetTimezone(const nsACString& aTimezone)
+{
+    mTimezone.Assign(aTimezone);
+    if (aTimezone.EqualsLiteral("UTC") ||
+        aTimezone.EqualsLiteral("utc"))
+    {
+        mTimezone.Truncate();
+        mIsUtc = PR_TRUE;
+    } else if (!aTimezone.IsEmpty()) {
+        mIsUtc = PR_FALSE;
+    }
+
+    return NS_OK;
+}
 
 NS_IMETHODIMP
 calDateTime::GetNativeTime(PRTime *aResult)