Add blink_gc_plugin variable to enable the clang plugin for checking GC consistency.

Source/config.gyp

 #
 # Copyright (C) 2013 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
@@ skipping 14 matching lines @@
 # DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #
 {
   'variables': {
     # If set to 1, doesn't compile debug symbols into webcore reducing the
     # size of the binary and increasing the speed of gdb.  gcc only.
     'remove_webcore_debug_symbols%': 0,
+    # Set to 1 to enable the clang plugin that checks the usage of the Blink
+    # garbage-collection infrastructure during compilation.
+    # Requires building locally since GOMA doesn't yet support the plugin.
+    'blink_gc_plugin%': 0,
   },
   'targets': [
   {
     'target_name': 'config',
     'type': 'none',
     'direct_dependent_settings': {
       'include_dirs': [
         '.',
         '..',
       ],
@@ skipping 46 matching lines @@
           # Due to a bug in gcc arm, we get warnings about uninitialized
           # timesNewRoman.unstatic.3258 and colorTransparent.unstatic.4879.
           'cflags': ['-Wno-uninitialized'],
         }],
         ['clang==1', {
           'cflags': ['-Wglobal-constructors'],
           'xcode_settings': {
             'WARNING_CFLAGS': ['-Wglobal-constructors'],
           },
         }],
+        # Only enable the blink_gc_plugin when using clang and chrome plugins.
+        ['blink_gc_plugin==1 and clang==1 and clang_use_chrome_plugins==1 and OS!="win"', {

[Mads Ager (chromium), 2014/01/10 10:50:45]

Is the OS!="win" needed? If we start using clang on Windows it seems that we
should use the plugins as well.

Do we want the use_chrome_plugins part? Do we rely on anything that is only
there when clang_use_chrome_plugins is set?

[zerny-chromium, 2014/01/10 11:33:59]

Currently build/common.gypi [1] only defines the plugin flags when not on
windows. I'm not sure that the setup actually works if clang==1 and OS=="win"
since there are unguarded uses of the variables being defined under the
assumption that OS!="win".

I'll remove the OS!="win" condition here, since if clang_blink_gc_plugin_flags
is properly defined for windows then this code works too.

The clang_use_chrome_plugins variable is default enabled but is used to disable
plugins if need be, eg, when running the type profiler which is a different
clang build IFAICT.

I think we should keep that condition because if the exisiting plugin does not
work with the type profiler then I doubt this one will.

[1] https://codereview.chromium.org/133463002/diff/70001/build/common.gypi

+          'cflags': ['<@(clang_blink_gc_plugin_flags)'],
+        }],
       ],
     },
   },
   {
     'target_name': 'unittest_config',
     'type': 'none',
     'dependencies': [
       'config',
       '<(DEPTH)/testing/gmock.gyp:gmock',
       '<(DEPTH)/testing/gtest.gyp:gtest',
     ],
     'export_dependent_settings': [
       'config',
       '<(DEPTH)/testing/gmock.gyp:gmock',
       '<(DEPTH)/testing/gtest.gyp:gtest',
     ],
     'direct_dependent_settings': {
       'cflags!': ['-Wglobal-constructors'],
       'xcode_settings': {
         'WARNING_CFLAGS!': ['-Wglobal-constructors'],
       },
     },
   }
   ],
 }