Make delegated software renderer work on Mac

content/renderer/gpu/compositor_software_output_device.cc

Index: content/renderer/gpu/compositor_software_output_device.cc
diff --git a/content/renderer/gpu/compositor_software_output_device.cc b/content/renderer/gpu/compositor_software_output_device.cc
index a8c893b18d3bc0583f6a00a75f77b2a19792707d..4d66f2680781b291e27a0bf834f03da6c2b5462f 100644
--- a/content/renderer/gpu/compositor_software_output_device.cc
+++ b/content/renderer/gpu/compositor_software_output_device.cc
@@ -94,10 +94,14 @@ size_t CompositorSoftwareOutputDevice::FindFreeBuffer(size_t hint) {
   return buffers_.size() - 1;
 }
 
-void CompositorSoftwareOutputDevice::Resize(const gfx::Size& viewport_size) {
+void CompositorSoftwareOutputDevice::Resize(
+    const gfx::Size& viewport_pixel_size,
+    float scale_factor) {
   DCHECK(CalledOnValidThread());
 
-  if (viewport_size_ == viewport_size)
+  scale_factor_ = scale_factor;
+
+  if (viewport_size_ == viewport_pixel_size)
     return;
 
   // Keep non-ACKed buffers in awaiting_ack_ until they get acknowledged.
@@ -110,7 +114,7 @@ void CompositorSoftwareOutputDevice::Resize(const gfx::Size& viewport_size) {
 
   buffers_.clear();
   current_index_ = -1;
-  viewport_size_ = viewport_size;
+  viewport_size_ = viewport_pixel_size;
 }
 
 void CompositorSoftwareOutputDevice::DiscardBackbuffer() {