SkRecordDraw: skip draw ops when the clip is empty

src/record/SkRecorder.h

 #ifndef SkRecorder_DEFINED
 #define SkRecorder_DEFINED
 
 #include "SkCanvas.h"
 #include "SkRecord.h"
 #include "SkRecords.h"
 
 // SkRecorder provides an SkCanvas interface for recording into an SkRecord.
 
 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;
     void drawPoints(PointMode mode,
                     size_t count,
                     const SkPoint pts[],
                     const SkPaint& paint) SK_OVERRIDE;
     void drawRect(const SkRect& rect, const SkPaint& paint) SK_OVERRIDE;
     void drawOval(const SkRect& oval, const SkPaint&) SK_OVERRIDE;
     void drawRRect(const SkRRect& rrect, const SkPaint& paint) SK_OVERRIDE;
@@ skipping 64 matching lines @@
     void onPushCull(const SkRect& cullRect) SK_OVERRIDE;
     void onPopCull() SK_OVERRIDE;
 
 private:
     template <typename T>
     T* copy(const T*);
 
     template <typename T>
     T* copy(const T[], unsigned count);
 
+    const Mode fMode;
     SkRecord* fRecord;
 };
 
 #endif//SkRecorder_DEFINED