Support vtable_verify (new compiler option).

base/allocator/allocator.gyp

Index: base/allocator/allocator.gyp
diff --git a/base/allocator/allocator.gyp b/base/allocator/allocator.gyp
index e2c8ac0faeb383fd96b138b1f99b23c830ab21bb..8f14f3776cbbc0d7c397086ab9e384fd1c3cacca 100644
--- a/base/allocator/allocator.gyp
+++ b/base/allocator/allocator.gyp
@@ -394,6 +394,16 @@
               '-Wl,-u_ZN15HeapLeakChecker12IgnoreObjectEPKv,-u_ZN15HeapLeakChecker14UnIgnoreObjectEPKv',
           ]},
         }],
+        [ 'use_vtable_verify==1', {

[Mark Mentovai, 2012/08/14 21:31:54]

Since you’ve removed use_vtable_verify from common.gypi AND you haven’t provided
a default definition anywhere here, this will now cause gyp to throw an
exception

(except in the rare and unexpected case where a user has affirmatively set this
GYP variable manually in GYP_DEFINES, ~/.gyp/include.gypi, or -D.)

[Mark Mentovai, 2012/08/15 00:18:41]

You do need to provide a default definition of use_vtable_verify just as you had
done before in common.gypi. It can be in this file. It should look something
like

  'variables': {
    'use_vtable_verify%': 0,
  },

A run through the Chromium try servers should tell you whether you’ve gotten
this right, since as I mentioned, nothing elsewhere will be setting this GYP
variable.

+          'cflags': [
+            '-Wno-sign-compare',
+            '-Wno-unused-result',
+            '-fvtable-verify=preinit',
+          ],
+          'cflags!': [
+            '-fvtable-verify=std',

[Mark Mentovai, 2012/08/14 21:32:23]

If nothing is adding this option any more, you can remove the cflags! that
excludes it.

[Mark Mentovai, 2012/08/15 00:18:41]

How would cflags ever contain -fvtable-verify=std? Nothing anywhere in the GYP
files ever specifies it.

+          ],
+        }],
         [ 'linux_use_debugallocation==1', {
           'sources!': [
             # debugallocation.cc #includes tcmalloc.cc,