Allocator shim skeleton + Linux impl behind a build flag

base/process/memory_linux.cc

Index: base/process/memory_linux.cc
diff --git a/base/process/memory_linux.cc b/base/process/memory_linux.cc
index b5c964084870a927d8adb60e8692f4b6fa5819d7..9fb630b4750bff97a952850c655b8159fe9c075d 100644
--- a/base/process/memory_linux.cc
+++ b/base/process/memory_linux.cc
@@ -8,6 +8,8 @@
 
 #include <new>
 
+#include "base/allocator/allocator_shim.h"
+#include "base/allocator/features.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/logging.h"
@@ -41,8 +43,12 @@ void OnNoMemory() {
 
 }  // namespace
 
+// TODO(primiano): Once the unified shim is on by default (crbug.com/550886)
+// get rid of the code in this entire #if section. The whole termination-on-OOM
+// logic is implemented in the shim.
 #if !defined(ADDRESS_SANITIZER) && !defined(MEMORY_SANITIZER) && \
-    !defined(THREAD_SANITIZER) && !defined(LEAK_SANITIZER)
+    !defined(THREAD_SANITIZER) && !defined(LEAK_SANITIZER) &&    \
+    !BUILDFLAG(USE_EXPERIMENTAL_ALLOCATOR_SHIM)
 
 #if defined(LIBC_GLIBC) && !defined(USE_TCMALLOC)
 
@@ -150,7 +156,10 @@ void EnableTerminationOnOutOfMemory() {
   // If we're using glibc's allocator, the above functions will override
   // malloc and friends and make them die on out of memory.
 #endif
-#if defined(USE_TCMALLOC)
+
+#if BUILDFLAG(USE_EXPERIMENTAL_ALLOCATOR_SHIM)
+  allocator::SetCallNewHandlerOnMallocFailure(true);
+#elif defined(USE_TCMALLOC)
   // For tcmalloc, we need to tell it to behave like new.
   tc_set_new_mode(1);
 #endif
@@ -194,7 +203,9 @@ bool AdjustOOMScore(ProcessId process, int score) {
 }
 
 bool UncheckedMalloc(size_t size, void** result) {
-#if defined(MEMORY_TOOL_REPLACES_ALLOCATOR) || \
+#if BUILDFLAG(USE_EXPERIMENTAL_ALLOCATOR_SHIM)
+  *result = allocator::UncheckedAlloc(size);
+#elif defined(MEMORY_TOOL_REPLACES_ALLOCATOR) || \
     (!defined(LIBC_GLIBC) && !defined(USE_TCMALLOC))
   *result = malloc(size);
 #elif defined(LIBC_GLIBC) && !defined(USE_TCMALLOC)