mac: Remove GPU bug workarounds for OS X versions before 10.9

gpu/command_buffer/tests/gl_iosurface_readback_workaround_unittest.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef GL_GLEXT_PROTOTYPES
 #define GL_GLEXT_PROTOTYPES
 #endif
 
 #include <GLES2/gl2.h>
 #include <GLES2/gl2ext.h>
@@ skipping 11 matching lines @@
 
 #if defined(OS_MACOSX)
 // A test that exercises the glReadPixels workaround for IOSurface backed
 // textures.
 class GLIOSurfaceReadbackWorkaroundTest : public testing::Test {
  public:
   GLIOSurfaceReadbackWorkaroundTest() {}
 
  protected:
   void SetUp() override {
-      base::CommandLine command_line(0, NULL);
-      command_line.AppendSwitchASCII(
-          switches::kGpuDriverBugWorkarounds,
-          base::IntToString(gpu::IOSURFACE_READBACK_WORKAROUND));
-      gl_.InitializeWithCommandLine(GLManager::Options(), command_line);
-      gl_.set_use_iosurface_memory_buffers(true);
-      DCHECK(gl_.workarounds().iosurface_readback_workaround);
+    base::CommandLine command_line(0, NULL);
+    gl_.InitializeWithCommandLine(GLManager::Options(), command_line);
+    gl_.set_use_iosurface_memory_buffers(true);
   }
 
   void TearDown() override {
     GLTestHelper::CheckGLError("no errors", __LINE__);
     gl_.Destroy();
   }
 
   GLManager gl_;
 };
 
@@ skipping 33 matching lines @@
 
   glReleaseTexImage2DCHROMIUM(source_target, image_id);
   glDestroyImageCHROMIUM(image_id);
   glDeleteTextures(1, &source_texture);
   glDeleteFramebuffers(1, &framebuffer);
 }
 
 #endif  // defined(OS_MACOSX)
 
 }  // namespace gpu