Enable whole-program virtual function optimization in LTO mode.

build/config/sanitizers/sanitizers.gni

Index: build/config/sanitizers/sanitizers.gni
diff --git a/build/config/sanitizers/sanitizers.gni b/build/config/sanitizers/sanitizers.gni
index fd0989faca6adb7b3d63ce91d998e575826302c4..f407498ef53f01e1afdc8e30d17331fc2a73ebda 100644
--- a/build/config/sanitizers/sanitizers.gni
+++ b/build/config/sanitizers/sanitizers.gni
@@ -39,6 +39,8 @@ declare_args() {
 
   # Compile with Control Flow Integrity to protect virtual calls and casts.
   # See http://clang.llvm.org/docs/ControlFlowIntegrity.html
+  #
+  # TODO(pcc): Remove this flag if/when CFI is enabled in official builds.
   is_cfi = false
 
   # By default, Control Flow Integrity will crash the program if it detects a
@@ -72,10 +74,6 @@ declare_args() {
   use_custom_libcxx = (is_asan && is_linux) || is_tsan || is_msan || is_ubsan ||
                       is_ubsan_security || use_libfuzzer
 
-  # Enable Link Time Optimization (output programs runs faster,
-  # but linking is up to 5-20x slower.
-  is_lto = is_cfi
-
   use_sanitizer_coverage = use_libfuzzer
 }