SkRecordDraw: skip draw ops when the clip is empty

src/record/SkRecorder.h

Index: src/record/SkRecorder.h
diff --git a/src/record/SkRecorder.h b/src/record/SkRecorder.h
index bf317f3bef1550a1a1e793763d6488f65f7c9b9b..0f2162f9177db67bcfd9c062081bd4d7c0755a15 100644
--- a/src/record/SkRecorder.h
+++ b/src/record/SkRecorder.h
@@ -9,8 +9,17 @@
 
 class SkRecorder : public SkCanvas {
 public:
+    // SkRecorder can work in two modes:
+    //   write-only: only a core subset of SkCanvas operations (save/restore, clip, transform, draw)
+    //   are supported, and all of the readback methods on SkCanvas will probably fail or lie.
+    //
+    //   read-write: all methods should behave with similar semantics to SkCanvas.
+    //
+    // Write-only averages 10-20% faster, but you can't sensibly inspect the canvas while recording.
+    enum Mode { kWriteOnly_Mode, kReadWrite_Mode };
+
     // Does not take ownership of the SkRecord.
-    SkRecorder(SkRecord*, int width, int height);
+    SkRecorder(Mode mode, SkRecord*, int width, int height);
 
     void clear(SkColor) SK_OVERRIDE;
     void drawPaint(const SkPaint& paint) SK_OVERRIDE;
@@ -95,6 +104,7 @@ private:
     template <typename T>
     T* copy(const T[], unsigned count);
 
+    const Mode fMode;
     SkRecord* fRecord;
 };