small fix for perf regression in GrAtlasTextContext

src/gpu/GrBatchAtlas.cpp

Index: src/gpu/GrBatchAtlas.cpp
diff --git a/src/gpu/GrBatchAtlas.cpp b/src/gpu/GrBatchAtlas.cpp
index 53ed177431651343533162a4ee5f2283af6f83c6..0bcd2f9e06325cd81bcbcce2435d104a6f83b027 100644
--- a/src/gpu/GrBatchAtlas.cpp
+++ b/src/gpu/GrBatchAtlas.cpp
@@ -366,7 +366,8 @@ void GrBatchAtlas::setLastUseToken(AtlasID id, BatchToken batchToken) {
 }
 
 void GrBatchAtlas::setLastUseTokenBulk(const BulkUseTokenUpdater& updater, BatchToken batchToken) {
-    for (int i = 0; i < updater.fCount; i++) {
+    int count = updater.fPlotsToUpdate.count();
+    for (int i = 0; i < count; i++) {
         BatchPlot* plot = fPlotArray[updater.fPlotsToUpdate[i]];
         this->makeMRU(plot);
         plot->setLastUseToken(batchToken);