Fix two instances of missing cstring include.

THe affected files use memcpy and strcpy, but fail to include cstring
header. This code fails to build on Linux when using glibc newer than
2.29.

Bug: 1074286
Change-Id: If23073acd012d0515937a9e7dc9782e6cc7c72af
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2164887Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Piotr Tworek <ptworek@vewd.com>
Cr-Commit-Position: refs/heads/master@{#762759}

third_party/blink/renderer/platform/geometry/length.h

@@ -23,6 +23,8 @@
 #ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_GEOMETRY_LENGTH_H_
 #define THIRD_PARTY_BLINK_RENDERER_PLATFORM_GEOMETRY_LENGTH_H_
 
+#include <cstring>
+
 #include "third_party/blink/renderer/platform/geometry/layout_unit.h"
 #include "third_party/blink/renderer/platform/platform_export.h"
 #include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"

third_party/blink/renderer/platform/heap/name_traits.h

@@ -5,6 +5,8 @@
 #ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_HEAP_NAME_TRAITS_H_
 #define THIRD_PARTY_BLINK_RENDERER_PLATFORM_HEAP_NAME_TRAITS_H_
 
+#include <cstring>
+
 #include "build/build_config.h"
 #include "third_party/blink/renderer/platform/bindings/name_client.h"
 #include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"