linux: enable seccomp sandbox by default

It seems the best way to keep the seccomp sandbox working is to have
everyone's development environment have it on by default.  So we turn
on the seccomp sandbox, but only for non-official builds.

If the build-time flag is set: --disable-seccomp-sandbox turns it off.
If the build-time flag is *not* set: --enable-seccomp-sandbox turns it on.

BUG=36133

Review URL: http://codereview.chromium.org/1558003

git-svn-id: http://src.chromium.org/svn/trunk/src/build@43122 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

common.gypi

@@ -208,6 +208,10 @@
     # Disable TCMalloc's heapchecker.
     'linux_use_heapchecker%': 0,
 
+    # Turn on seccomp sandbox by default.
+    # (Note: this is disabled for official builds.)
+    'linux_use_seccomp_sandbox%': 1,
+
     # Set to select the Title Case versions of strings in GRD files.
     'use_titlecase_in_grd_files%': 0,
 
@@ -957,6 +961,9 @@
             'cflags': [ '-gstabs' ],
             'defines': ['USE_LINUX_BREAKPAD'],
           }],
+          ['linux_use_seccomp_sandbox==1 and buildtype!="Official"', {
+            'defines': ['USE_SECCOMP_SANDBOX'],
+          }],
           ['library=="shared_library"', {
             # When building with shared libraries, remove the visiblity-hiding
             # flag.