[ptr-compr] Fix false positive memory leak reports

... by adding use_unaligned=1 to default LSAN_OPTIONS.

With pointer compression in V8 the external pointers from V8 heap
are guaranteed to be only 4-byte aligned so without this flag
LSAN is not able to find all the external pointers.

Bug: chromium:328552
Change-Id: I4bb7eb68d023ae4fb4324cf13d317e3ee011669d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1926472Reviewed-by: Abhishek Arya <inferno@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718488}

build/sanitizers/sanitizer_options.cc

@@ -130,7 +130,15 @@ SANITIZER_HOOK_ATTRIBUTE const char *__msan_default_options() {
 //   strip_path_prefix=/../../ - prefixes up to and including this
 //     substring will be stripped from source file paths in symbolized reports.
 const char kLsanDefaultOptions[] =
-    "print_suppressions=1 strip_path_prefix=/../../ ";
+    "print_suppressions=1 strip_path_prefix=/../../ "
+#if defined(ARCH_CPU_64_BITS)
+    // When pointer compression in V8 is enabled the external pointers in the
+    // heap are guaranteed to be only 4 bytes aligned. So we need this option
+    // in order to ensure that LSAN will find all the external pointers.
+    // TODO(crbug.com/328552): see updates from 2019.
+    "use_unaligned=1 "
+#endif  // ARCH_CPU_64_BITS
+    ;
 
 SANITIZER_HOOK_ATTRIBUTE const char *__lsan_default_options() {
   return kLsanDefaultOptions;