Turn on full masking with untrusted-code-mitigations

Bug: chromium:856973
Change-Id: Ib0feeb18e27dc455ecf8547b3dd5bd284c39735a
Reviewed-on: https://chromium-review.googlesource.com/1225899Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56016}

src/flag-definitions.h

@@ -526,7 +526,7 @@ DEFINE_BOOL(untrusted_code_mitigations, V8_DEFAULT_UNTRUSTED_CODE_MITIGATIONS,
 #undef V8_DEFAULT_UNTRUSTED_CODE_MITIGATIONS
 
 DEFINE_BOOL(branch_load_poisoning, false, "Mask loads with branch conditions.")
-DEFINE_IMPLICATION(future, branch_load_poisoning)
+DEFINE_IMPLICATION(untrusted_code_mitigations, branch_load_poisoning)
 
 // Flags to help platform porters
 DEFINE_BOOL(minimal, false,