Use SkTArray for mailbox polling

The mailbox uses SkTArray internally, so swapping is optimal when dest
has no preallocated storage.

Change-Id: Ic295f3707d07c97b1881e775cac3a23a6b2fef71
Reviewed-on: https://skia-review.googlesource.com/9641
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>

src/gpu/text/GrTextBlobCache.h

@@ -169,8 +169,7 @@ private:
     void checkPurge(GrAtlasTextBlob* blob = nullptr) {
         // First, purge all stale blob IDs.
         {
-            // TODO: tweak poll to allow mem-movable arrays, and update.
-            SkSTArray<128, PurgeBlobMessage, false> msgs;
+            SkTArray<PurgeBlobMessage> msgs;
             fPurgeBlobInbox.poll(&msgs);
 
             for (const auto& msg : msgs) {