Update from https://crrev.com/320931

base/memory/BUILD.gn

Index: base/memory/BUILD.gn
diff --git a/base/memory/BUILD.gn b/base/memory/BUILD.gn
index 5d016ff681221bf14b12fab41c903b1ae8658a7a..3d4c22cd3d5f83bddc036abcfa3518e7294ac296 100644
--- a/base/memory/BUILD.gn
+++ b/base/memory/BUILD.gn
@@ -8,14 +8,10 @@ source_set("memory") {
     "aligned_memory.h",
     "discardable_memory.cc",
     "discardable_memory.h",
-    "discardable_memory_android.cc",
-    "discardable_memory_linux.cc",
-    "discardable_memory_mac.cc",
     "discardable_memory_shmem.cc",
     "discardable_memory_shmem.h",
     "discardable_memory_shmem_allocator.cc",
     "discardable_memory_shmem_allocator.h",
-    "discardable_memory_win.cc",
     "discardable_shared_memory.cc",
     "discardable_shared_memory.h",
     "linked_ptr.h",
@@ -58,7 +54,7 @@ source_set("memory") {
     sources -= [ "shared_memory_nacl.cc" ]
   }
 
-  defines = [ "BASE_IMPLEMENTATION" ]
+  configs += [ "//base:base_implementation" ]
 
   visibility = [ "//base/*" ]
 }