Add GrProgramElement base class for GrEffect with deferred exec ref.

src/gpu/GrProgramElement.cpp

+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+
+#include "GrProgramElement.h"
+#include "GrProgramResource.h"
+
+void GrProgramElement::convertRefToPendingExecution() const {
+    // This function makes it so that all the GrProgramResources own a single ref to their
+    // underlying GrGpuResource if there are any refs to the GrProgramElement and a single
+    // pending read/write if there are any pending executions of the GrProgramElement. The
+    // GrProgramResource will give up its single ref and/or pending read/write in its destructor.
+    SkASSERT(fRefCnt > 0);
+    if (0 == fPendingExecutions) {
+        for (int i = 0; i < fProgramResources.count(); ++i) {
+            fProgramResources[i]->markPendingIO();
+        }
+    }
+    ++fPendingExecutions;
+    this->unref();
+    if (0 == fRefCnt) {
+        for (int i = 0; i < fProgramResources.count(); ++i) {
+            fProgramResources[i]->removeRef();
+        }
+    }
+}