Fix for 300ms scroll lag on 2013 Mac Pros once idle for 10seconds

ui/gl/gl_context_cgl.cc

Index: ui/gl/gl_context_cgl.cc
diff --git a/ui/gl/gl_context_cgl.cc b/ui/gl/gl_context_cgl.cc
index 2fd20a086cbebc83ff8d157f2d8bbaa91acad501..9ec6facb67615c7f3c2ee5de404ac5adeb0a0085 100644
--- a/ui/gl/gl_context_cgl.cc
+++ b/ui/gl/gl_context_cgl.cc
@@ -31,14 +31,15 @@ struct CGLRendererInfoObjDeleter {
 
 }  // namespace
 
-static CGLPixelFormatObj GetPixelFormat() {
+static CGLPixelFormatObj GetPixelFormat(bool prevent_switchable) {
   static CGLPixelFormatObj format;
   if (format)
     return format;
   std::vector<CGLPixelFormatAttribute> attribs;
   // If the system supports dual gpus then allow offline renderers for every
-  // context, so that they can all be in the same share group.
-  if (ui::GpuSwitchingManager::GetInstance()->SupportsDualGpus()) {
+  // context, so that they can all be in the same share group. Don't do this for
+  // discrete GPUs to avoid being offloaded to an idle GPU by OSX.
+  if (!prevent_switchable) {
     attribs.push_back(kCGLPFAAllowOfflineRenderers);
     g_support_renderer_switching = true;
   }
@@ -93,14 +94,16 @@ bool GLContextCGL::Initialize(GLSurface* compatible_surface,
   GLContextCGL* share_context = share_group() ?
       static_cast<GLContextCGL*>(share_group()->GetContext()) : NULL;
 
-  CGLPixelFormatObj format = GetPixelFormat();
+  const bool prevent_switchable = gpu_preference == PreferDiscreteGpu ||
+      !ui::GpuSwitchingManager::GetInstance()->SupportsDualGpus();
+
+  CGLPixelFormatObj format = GetPixelFormat(prevent_switchable);
   if (!format)
     return false;
 
   // If using the discrete gpu, create a pixel format requiring it before we
   // create the context.
-  if (!ui::GpuSwitchingManager::GetInstance()->SupportsDualGpus() ||
-      gpu_preference == PreferDiscreteGpu) {
+  if (prevent_switchable) {
     std::vector<CGLPixelFormatAttribute> discrete_attribs;
     discrete_attribs.push_back((CGLPixelFormatAttribute) 0);
     GLint num_pixel_formats;
@@ -164,7 +167,7 @@ bool GLContextCGL::ForceGpuSwitchIfNeeded() {
       // Attempt to find a virtual screen that's using the requested renderer,
       // and switch the context to use that screen. Don't attempt to switch if
       // the context requires the discrete GPU.
-      CGLPixelFormatObj format = GetPixelFormat();
+      CGLPixelFormatObj format = GetPixelFormat(false);
       int virtual_screen_count;
       if (CGLDescribePixelFormat(format, 0, kCGLPFAVirtualScreenCount,
                                  &virtual_screen_count) != kCGLNoError)