WebRTC+libyuv: switch to use_allocator GYP variable.

masters/master.tryserver.libyuv/master.cfg

Index: masters/master.tryserver.libyuv/master.cfg
diff --git a/masters/master.tryserver.libyuv/master.cfg b/masters/master.tryserver.libyuv/master.cfg
index 21cd77f1225266f965fab4a6eaf222163683b621..a2ae7b592522b4e1ff8abfc0ffea29956908de64 100755
--- a/masters/master.tryserver.libyuv/master.cfg
+++ b/masters/master.tryserver.libyuv/master.cfg
@@ -41,7 +41,6 @@ def android():
   return libyuv_factory.LibyuvFactory('', 'linux2', nohooks_on_update=True,
                                       target_os='android')
 tests = ['libyuv_unittest']
-asan_gyp_defines = 'asan=1 release_extra_cflags=-g linux_use_tcmalloc=0'
 options = ['--clobber-post-fail']
 ninja_options = options + ['--build-tool=ninja']
 win_factory_prop = {
@@ -129,7 +128,7 @@ b_mac_asan = {
         tests=tests,
         factory_properties={
             'asan': True,
-            'gclient_env': {'GYP_DEFINES': asan_gyp_defines},
+            'gclient_env': {'GYP_DEFINES': 'asan=1 release_extra_cflags=-g'},
         })
 }
 
@@ -205,7 +204,9 @@ b_linux_asan = {
         tests=tests,
         factory_properties={
             'asan': True,
-            'gclient_env': {'GYP_DEFINES': asan_gyp_defines},
+            'gclient_env': {'GYP_DEFINES': ('asan=1 release_extra_cflags=-g '
+                                            'use_allocator=none'),
+            },
         })
 }