first draft of error checking / reporting API

include/core/SkError.h

+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+ 
+#ifndef SkError_DEFINED
+#define SkError_DEFINED
+
+typedef enum {
+    kError_NoError=0,
+    kError_InvalidArgument,
+    kError_InvalidOperation,
+    kError_InvalidHandle,
+    kError_InvalidPaint,
+    kError_OutOfMemory,
+    kError_ParseError
+} SkError;
+
+SkError SkGetLastError();
+void SkClearLastError();
+typedef void (*SkErrorCallbackFunction)(SkError, void *);
+
+void SkSetErrorCallback(SkErrorCallbackFunction cb, void *context);
+const char *SkGetLastErrorString();
+
+#endif /* SkError_DEFINED */