add SkPixmap and external locking to bitmaps

src/core/SkPixmap.cpp

Index: src/core/SkPixmap.cpp
diff --git a/src/core/SkPixmap.cpp b/src/core/SkPixmap.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..2d15e8a1857ba9f93a3862a9bfddc4e383bc0b6c
--- /dev/null
+++ b/src/core/SkPixmap.cpp
@@ -0,0 +1,18 @@
+/*
+ * 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 "SkPixmap.h"
+
+void SkAutoPixmapUnlock::reset(const SkPixmap& pm, void (*unlock)(void*), void* ctx) {
+    SkASSERT(pm.addr() != NULL);
+
+    this->unlock();
+    fPixmap = pm;
+    fUnlockProc = unlock;
+    fUnlockContext = ctx;
+    fIsLocked = true;
+}