Use the generic heap shim with SyzyASAN.

This allows the generic shim to supply malloc_unchecked, which in turn fixes base::UncheckedMalloc so it returns nullptr instead of barfing on OOM.

BUG=627455
R=chrisha@chromium.org
TBR=brettw@chromium.org

Review-Url: https://codereview.chromium.org/2385713002
Cr-Original-Commit-Position: refs/heads/master@{#422138}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 4d1f56888c68dcda9aa4ad7045b71a6c0eb5969d

config/BUILD.gn

@@ -260,7 +260,6 @@ config("feature_flags") {
   if (is_syzyasan) {
     defines += [
       "SYZYASAN",
-      "MEMORY_TOOL_REPLACES_ALLOCATOR",
       "MEMORY_SANITIZER_INITIAL_SIZE",
     ]
   }

config/allocator.gni

@@ -17,7 +17,7 @@ if (is_android || current_cpu == "mipsel" || is_mac || is_ios || is_asan ||
 # the shim. NaCl in particular does seem to link some binaries statically
 # against the debug CRT with "is_nacl=false".
 if ((is_linux || is_android || (is_win && !is_component_build && !is_debug)) &&
-    !is_syzyasan && !is_asan && !is_lsan && !is_tsan && !is_msan) {
+     !is_asan && !is_lsan && !is_tsan && !is_msan) {
   _default_use_experimental_allocator_shim = true
 } else {
   _default_use_experimental_allocator_shim = false