Make GrVertexBatch objects hold their own draws during GrDrawTarget flush

tests/GrPorterDuffTest.cpp

Index: tests/GrPorterDuffTest.cpp
diff --git a/tests/GrPorterDuffTest.cpp b/tests/GrPorterDuffTest.cpp
index 34dd12bc0f213c70a895a1ce1ababab7a3a79efa..b40ae7cc94b6cc120f2ec365e1824faa7197234f 100644
--- a/tests/GrPorterDuffTest.cpp
+++ b/tests/GrPorterDuffTest.cpp
@@ -911,7 +911,7 @@ static void test_lcd_coverage(skiatest::Reporter* reporter, const GrCaps& caps)
         const char* name() const override { return "Test LCD Text Batch"; }
         void initBatchTracker(const GrPipelineOptimizations&) override {}
         bool onCombineIfPossible(GrBatch*, const GrCaps&) override  { return false; }
-        void generateGeometry(GrBatchTarget*) override {}
+        void onPrepareDraws(Target*) override {};
 
     } testLCDCoverageBatch;