SkRecord: make culling work if SkRecordAnnotateCullingPairs is called.

src/record/SkRecordCulling.cpp

Index: src/record/SkRecordCulling.cpp
diff --git a/src/record/SkRecordCulling.cpp b/src/record/SkRecordCulling.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..e866bd82cb85ed821ebb1c8e3eca21d842656d6f
--- /dev/null
+++ b/src/record/SkRecordCulling.cpp
@@ -0,0 +1,38 @@
+#include "SkRecordCulling.h"
+
+#include "SkRecords.h"
+#include "SkTDArray.h"
+
+namespace {
+
+struct Annotator {
+    unsigned index;
+    SkTDArray<SkRecords::PushCull*> pushStack;
+
+    // Do nothing to most record types.
+    template <typename T> void operator()(T*) {}
+};
+
+template <> void Annotator::operator()(SkRecords::PushCull* push) {
+    // Store the push's index for now.  We'll calculate the offset using this in the paired pop.
+    push->popOffset = index;
+    pushStack.push(push);
+}
+
+template <> void Annotator::operator()(SkRecords::PopCull* pop) {
+    SkRecords::PushCull* push = pushStack.top();
+    pushStack.pop();
+
+    SkASSERT(index > push->popOffset);          // push->popOffset holds the index of the push.
+    push->popOffset = index - push->popOffset;  // Now it's the offset between push and pop.
+}
+
+}  // namespace
+
+void SkRecordAnnotateCullingPairs(SkRecord* record) {
+    Annotator annotator;
+
+    for (annotator.index = 0; annotator.index < record->count(); annotator.index++) {
+        record->mutate(annotator.index, annotator);
+    }
+}