Add a bench to measure SkPictureRecorder constant overhead.

bench/PictureOverheadBench.cpp

Index: bench/PictureOverheadBench.cpp
diff --git a/bench/PictureOverheadBench.cpp b/bench/PictureOverheadBench.cpp
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index 0000000000000000000000000000000000000000..884b005ee7f5f09dd74a5066311ab295655d6e21
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+++ b/bench/PictureOverheadBench.cpp
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+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+// A benchmark designed to isolate the constant overheads of picture recording.
+// We record a very tiny (one op) picture; one op is better than none, as it forces
+// us to allocate memory to store that op... we can't just cheat by holding onto NULLs.
+
+#include "Benchmark.h"
+#include "SkCanvas.h"
+#include "SkPictureRecorder.h"
+
+struct PictureOverheadBench : public Benchmark {
+    const char* onGetName() override { return "picture_overhead"; }
+    bool isSuitableFor(Backend backend) override { return backend == kNonRendering_Backend; }
+
+    void onDraw(const int loops, SkCanvas*) override {
+        SkPictureRecorder rec;
+        for (int i = 0; i < loops; i++) {
+            SkCanvas* c = rec.beginRecording(SkRect::MakeWH(2000,3000));
+                c->drawRect(SkRect::MakeXYWH(10, 10, 1000, 1000), SkPaint());
+            SkAutoTUnref<SkPicture> pic(rec.endRecordingAsPicture());
+        }
+    }
+};
+DEF_BENCH(return new PictureOverheadBench;)