Fix typo of the std::aligned_alloc name in comment

Also add a caveat about a restriction of std::aligned_alloc on its size
parameter (size must be an integral multiple of alignment).

Change-Id: I83389f78650bf51e819d4f992789f0361a4b29db
Reviewed-on: https://chromium-review.googlesource.com/1232633Reviewed-by: Mark Mentovai <mark@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592394}

base/memory/aligned_memory.h

@@ -34,7 +34,9 @@
 
 namespace base {
 
-// This can be replaced with std::aligned_malloc when we have C++17.
+// This can be replaced with std::aligned_alloc when we have C++17.
+// Caveat: std::aligned_alloc requires the size parameter be an integral
+// multiple of alignment.
 BASE_EXPORT void* AlignedAlloc(size_t size, size_t alignment);
 
 inline void AlignedFree(void* ptr) {