Bug 1276947: Environment variable to force the use of the crash guard in nightly. r=dvander

MozReview-Commit-ID: 22O5Qtd0VUZ

--HG--
extra : rebase_source : bceca8e9e74db4a7f40dbafd5f02c22e98b5d695

gfx/src/DriverCrashGuard.cpp

@@ -69,8 +69,9 @@ AreCrashGuardsEnabled()
 #ifdef NIGHTLY_BUILD
   // We only use the crash guard on non-nightly channels, since the nightly
   // channel is for development and having graphics features perma-disabled
-  // is rather annoying.
-  return false;
+  // is rather annoying.  Unless the user forces is with an environment
+  // variable, which comes in handy for testing.
+  return gfxEnv::ForceCrashGuardNightly();
 #else
   // Check to see if all guards have been disabled through the environment.
   if (gfxEnv::DisableCrashGuard()) {

gfx/thebes/gfxEnv.h

@@ -47,6 +47,7 @@ public:
 
   // Disabling the crash guard in DriverCrashGuard
   DECL_GFX_ENV_ONCE("MOZ_DISABLE_CRASH_GUARD", DisableCrashGuard);
+  DECL_GFX_ENV_ONCE("MOZ_FORCE_CRASH_GUARD_NIGHTLY", ForceCrashGuardNightly);
 
   // We force present to work around some Windows bugs - disable that if this
   // environment variable is set.