Run mixedxfermodes GM through the pipe.

Pass the size of the GM to SkGPipeWriter.startRecording(), so that
calls to getDeviceSize() on the returned SkCanvas return a reasonable
result. This allows removing the flag to skip mixedxfermodes.

BUG=https://code.google.com/p/skia/issues/detail?id=1199

Review URL: https://codereview.chromium.org/13814023

git-svn-id: http://skia.googlecode.com/svn/trunk@8598 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gm/gmmain.cpp b/gm/gmmain.cpp
index 5b0f662..8cb74be 100644
--- a/gm/gmmain.cpp
+++ b/gm/gmmain.cpp
@@ -1035,7 +1035,8 @@
                 PipeController pipeController(&canvas);
                 SkGPipeWriter writer;
                 SkCanvas* pipeCanvas = writer.startRecording(&pipeController,
-                                                             gPipeWritingFlagCombos[i].flags);
+                                                             gPipeWritingFlagCombos[i].flags,
+                                                             size.width(), size.height());
                 if (!simulateFailure) {
                     invokeGM(gm, pipeCanvas, false, false);
                 }
@@ -1073,7 +1074,8 @@
                 TiledPipeController pipeController(bitmap);
                 SkGPipeWriter writer;
                 SkCanvas* pipeCanvas = writer.startRecording(&pipeController,
-                                                             gPipeWritingFlagCombos[i].flags);
+                                                             gPipeWritingFlagCombos[i].flags,
+                                                             size.width(), size.height());
                 invokeGM(gm, pipeCanvas, false, false);
                 complete_bitmap(&bitmap);
                 writer.endRecording();