Remove -fsanitize=null for ubsan_vptr=1 build.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index db01f93e0664e2469b03eff81e6dc1c8e1a7b1c4..c06e74dcb6d07f522c665f4fbdcb431667c659f1 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -396,7 +396,7 @@
       # See http://clang.llvm.org/docs/UsersManual.html
       'ubsan%': 0,
 
-      # Enable building with UBsan's vptr (Clang's -fsanitize=vptr -fsanitize=null options).
+      # Enable building with UBsan's vptr (Clang's -fsanitize=vptr option).
       # -fsanitize=vptr only works with clang, but ubsan_vptr=1 implies clang=1
       'ubsan_vptr%': 0,
       'ubsan_vptr_blacklist%': '<(PRODUCT_DIR)/../../tools/ubsan_vptr/blacklist.txt',
@@ -4032,7 +4032,6 @@
               ['_toolset=="target"', {
                 'cflags': [
                   '-fsanitize=vptr',
-                  '-fsanitize=null',  # Avoid dereferences on null pointer objects.
                   '-fsanitize-blacklist=<(ubsan_vptr_blacklist)',
                 ],
                 'cflags_cc!': [
@@ -4042,7 +4041,7 @@
                   '-fno-rtti',
                 ],
                 'ldflags': [
-                  '-fsanitize=vptr',  # -fsanitize=null is not necessary.
+                  '-fsanitize=vptr',
                 ],
                 'defines': [
                   'UNDEFINED_SANITIZER',