ozone: Implement zero/one-copy texture for Ozone GBM.

content/common/gpu/client/gpu_memory_buffer_impl_ozone_native_pixmap.cc

Index: content/common/gpu/client/gpu_memory_buffer_impl_ozone_native_pixmap.cc
diff --git a/content/common/gpu/client/gpu_memory_buffer_impl_ozone_native_pixmap.cc b/content/common/gpu/client/gpu_memory_buffer_impl_ozone_native_pixmap.cc
index 40500a604f8a10ed40790cccb67a61348d455023..214cddd281f23f1c5ed760cdc3cfbbcd5196647e 100644
--- a/content/common/gpu/client/gpu_memory_buffer_impl_ozone_native_pixmap.cc
+++ b/content/common/gpu/client/gpu_memory_buffer_impl_ozone_native_pixmap.cc
@@ -36,11 +36,17 @@ GpuMemoryBufferImplOzoneNativePixmap::CreateFromHandle(
 }
 
 bool GpuMemoryBufferImplOzoneNativePixmap::Map(void** data) {
-  return pixmap_->Map(data);
+  DCHECK(!mapped_);

[reveman, 2015/08/07 17:59:44]

Looks like you already have this dcheck in the pixmap implementation. Why are
you also adding it here? One dcheck is enough.

[dshwang, 2015/08/11 17:44:56]

All GpuMemoryBufferImplXXX::Map/Unmap has same dcheck, so it's a bit weird that
only this doesn't have the dcheck.
On the other hands, I'm reluctant to remove dcheck in
ClientNativePixmapVgem::Map/Unmap because the dcheck helps to understand code.

[reveman, 2015/08/11 18:53:52]

Other implementations have DCHECKs as we're not in control over the API they are
calling into and can make sure they crash in a reliable way when used
inappropriately. We're in control over the ClientNativePixmap API and able to
make sure that inappropriate use is handled correctly. I don't think DCHECKs
here are needed here for that reason.

[dshwang, 2015/08/11 19:36:06]

Done. Thank you for patient explanation.

+  bool result = pixmap_->Map(data);
+  if (result)
+    mapped_ = true;
+  return result;
 }
 
 void GpuMemoryBufferImplOzoneNativePixmap::Unmap() {
+  DCHECK(mapped_);
   pixmap_->Unmap();
+  mapped_ = false;
 }
 
 void GpuMemoryBufferImplOzoneNativePixmap::GetStride(int* stride) const {