Use GpuPreferences to avoid directly accessing switches in gpu related code

gpu/command_buffer/service/context_group_unittest.cc

Index: gpu/command_buffer/service/context_group_unittest.cc
diff --git a/gpu/command_buffer/service/context_group_unittest.cc b/gpu/command_buffer/service/context_group_unittest.cc
index 50b67649dfee3a4ede43c97461a3b8e784795ee2..f343e5e2e5853464ae9fc7d3cd3d6e3fb6e0a33b 100644
--- a/gpu/command_buffer/service/context_group_unittest.cc
+++ b/gpu/command_buffer/service/context_group_unittest.cc
@@ -43,9 +43,11 @@ class ContextGroupTest : public GpuServiceTest {
     GpuServiceTest::SetUp();
     decoder_.reset(new MockGLES2Decoder());
     group_ = scoped_refptr<ContextGroup>(new ContextGroup(
-        NULL, NULL, NULL, NULL, NULL, NULL, NULL, kBindGeneratesResource));
+        gpu_preferences_, NULL, NULL, NULL, NULL, NULL, NULL, NULL,
+        kBindGeneratesResource));
   }
 
+  GpuPreferences gpu_preferences_;
   scoped_ptr<MockGLES2Decoder> decoder_;
   scoped_refptr<ContextGroup> group_;
 };