Add a means of extracting active operations from SkPicture

src/core/SkPicture.cpp

Index: src/core/SkPicture.cpp
===================================================================
--- src/core/SkPicture.cpp	(revision 13850)
+++ src/core/SkPicture.cpp	(working copy)
@@ -264,6 +264,19 @@
     SkASSERT(NULL == fRecord);
 }
 
+const SkPicture::OperationList& SkPicture::OperationList::InvalidList() {
+    static OperationList gInvalid;
+    return gInvalid;
+}
+
+const SkPicture::OperationList& SkPicture::EXPERIMENTAL_getActiveOps(const SkIRect& queryRect) {
+    this->endRecording();
+    if (NULL != fPlayback) {
+        return fPlayback->getActiveOps(queryRect);
+    }
+    return OperationList::InvalidList();
+}
+
 void SkPicture::draw(SkCanvas* surface, SkDrawPictureCallback* callback) {
     this->endRecording();
     if (NULL != fPlayback) {