clang/win: Build without -Wno-null-dereference.

BUG=505300

Review URL: https://codereview.chromium.org/1216903002

Cr-Original-Commit-Position: refs/heads/master@{#336717}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 6f856f785833aae16732c3573ef4174561ce7de4

common.gypi

@@ -5714,7 +5714,6 @@
                   '-Wno-missing-braces',  # http://crbug.com/505297
                   '-Wno-missing-declarations',  # http://crbug.com/505298
                   '-Wno-msvc-include',  # http://crbug.com/505299
-                  '-Wno-null-dereference',  # http://crbug.com/505300
                   '-Wno-overloaded-virtual',  # http://crbug.com/505301
                   '-Wno-parentheses',  # http://crbug.com/505302
                   '-Wno-pointer-sign',  # http://crbug.com/505303

config/compiler/BUILD.gn

@@ -813,7 +813,6 @@ if (is_win) {
       "-Wno-missing-braces",  # http://crbug.com/505297
       "-Wno-missing-declarations",  # http://crbug.com/505298
       "-Wno-msvc-include",  # http://crbug.com/505299
-      "-Wno-null-dereference",  # http://crbug.com/
       "-Wno-overloaded-virtual",  # http://crbug.com/505301
       "-Wno-parentheses",  # http://crbug.com/505302
       "-Wno-pointer-sign",  # http://crbug.com/505303