SkSemaphore: use SYNC_POLICY_LIFO on Mach.

src/core/SkSemaphore.cpp

Index: src/core/SkSemaphore.cpp
diff --git a/src/core/SkSemaphore.cpp b/src/core/SkSemaphore.cpp
index 3f19d4fa1239317dcbdfb8bded836419c02818da..ac62930082d553fb8473618134fa2a932e423931 100644
--- a/src/core/SkSemaphore.cpp
+++ b/src/core/SkSemaphore.cpp
@@ -13,7 +13,7 @@
         semaphore_t fSemaphore;
 
         OSSemaphore()  {
-            semaphore_create(mach_task_self(), &fSemaphore, SYNC_POLICY_FIFO, 0/*initial count*/);
+            semaphore_create(mach_task_self(), &fSemaphore, SYNC_POLICY_LIFO, 0/*initial count*/);
         }
         ~OSSemaphore() { semaphore_destroy(mach_task_self(), fSemaphore); }