Run mixedxfermodes GM through the pipe.

gm/gmmain.cpp

Index: gm/gmmain.cpp
diff --git a/gm/gmmain.cpp b/gm/gmmain.cpp
index 850106408c9026d55024bbc04001ba6a12840071..9aab06d4863b52f3762e06168923511ded061bc3 100644
--- a/gm/gmmain.cpp
+++ b/gm/gmmain.cpp
@@ -1008,8 +1008,9 @@ public:
             installFilter(&canvas);
             PipeController pipeController(&canvas);
             SkGPipeWriter writer;
-            SkCanvas* pipeCanvas = writer.startRecording(
-              &pipeController, gPipeWritingFlagCombos[i].flags);
+            SkCanvas* pipeCanvas = writer.startRecording(&pipeController,
+                                                         gPipeWritingFlagCombos[i].flags,
+                                                         size.width(), size.height());
             if (!simulateFailure) {
                 invokeGM(gm, pipeCanvas, false, false);
             }
@@ -1037,8 +1038,9 @@ public:
             installFilter(&canvas);
             TiledPipeController pipeController(bitmap);
             SkGPipeWriter writer;
-            SkCanvas* pipeCanvas = writer.startRecording(
-              &pipeController, gPipeWritingFlagCombos[i].flags);
+            SkCanvas* pipeCanvas = writer.startRecording(&pipeController,
+                                                         gPipeWritingFlagCombos[i].flags,
+                                                         size.width(), size.height());
             invokeGM(gm, pipeCanvas, false, false);
             complete_bitmap(&bitmap);
             writer.endRecording();