Add sk_calloc. Remove SkMemory_stdlib, which seems unused.

include/core/SkTypes.h

Index: include/core/SkTypes.h
diff --git a/include/core/SkTypes.h b/include/core/SkTypes.h
index 039369119e6fd32313d56cc088712bf223ed8ccd..f2245184e66cd38e3b1169a99b807d5f2615e163 100644
--- a/include/core/SkTypes.h
+++ b/include/core/SkTypes.h
@@ -49,7 +49,7 @@ enum {
 };
 /** Return a block of memory (at least 4-byte aligned) of at least the
     specified size. If the requested memory cannot be returned, either
-    return null (if SK_MALLOC_TEMP bit is clear) or call sk_throw()
+    return null (if SK_MALLOC_TEMP bit is clear) or throw an exception
     (if SK_MALLOC_TEMP bit is set). To free the memory, call sk_free().
 */
 SK_API extern void* sk_malloc_flags(size_t size, unsigned flags);
@@ -64,6 +64,14 @@ SK_API extern void* sk_realloc_throw(void* buffer, size_t size);
 */
 SK_API extern void sk_free(void*);
 
+/** Much like calloc: returns a pointer to at least size zero bytes, or NULL on failure.
+ */
+SK_API extern void* sk_calloc(size_t size);
+
+/** Same as sk_calloc, but throws an exception instead of returning NULL on failure.
+ */
+SK_API extern void* sk_calloc_throw(size_t size);
+
 // bzero is safer than memset, but we can't rely on it, so... sk_bzero()
 static inline void sk_bzero(void* buffer, size_t size) {
     memset(buffer, 0, size);