Add an Allocator interface that indicates if memory is zero init

tools/android/SkBRDAllocator.h

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkBitmap.h"
+#include "SkCodec.h"
+
+/**
+ *  Abstract subclass of SkBitmap's allocator.
+ *  Allows the allocator to indicate if the memory it allocates
+ *  is zero initialized.
+ */
+class SkBRDAllocator : public SkBitmap::Allocator {
+public:
+
+    /**
+     *  Indicates if the memory allocated by this allocator is
+     *  zero initialized.
+     */
+    virtual SkCodec::ZeroInitialized zeroInit() const = 0;
+};