Make SkTime SK_API so that SkTime::GetDateTime() is visible to the clients.

include/core/SkTime.h

Index: include/core/SkTime.h
diff --git a/include/core/SkTime.h b/include/core/SkTime.h
index 8a8224a82a564437c58c3a3b313e53e28cbdf985..e9a894812b83f9eb1003356715204e66c2ec09b9 100644
--- a/include/core/SkTime.h
+++ b/include/core/SkTime.h
@@ -17,7 +17,7 @@ class SkString;
 /** \class SkTime
     Platform-implemented utilities to return time of day, and millisecond counter.
 */
-class SkTime {
+class SK_API SkTime {
 public:
     struct DateTime {
         int16_t  fTimeZoneMinutes;  // The number of minutes that GetDateTime()