zero-copy: Clarify to allocate/destroy GpuMemoryBuffer on any thread and use it on the main thread o

ui/ozone/gpu/gpu_memory_buffer_factory_ozone_native_buffer.cc

Index: ui/ozone/gpu/gpu_memory_buffer_factory_ozone_native_buffer.cc
diff --git a/ui/ozone/gpu/gpu_memory_buffer_factory_ozone_native_buffer.cc b/ui/ozone/gpu/gpu_memory_buffer_factory_ozone_native_buffer.cc
index 38667e51e180f2d306fc50ec87e8994da9d88e1f..b265c9176c9679f6176306c4898e57dd1b1065e5 100644
--- a/ui/ozone/gpu/gpu_memory_buffer_factory_ozone_native_buffer.cc
+++ b/ui/ozone/gpu/gpu_memory_buffer_factory_ozone_native_buffer.cc
@@ -138,6 +138,7 @@ bool GpuMemoryBufferFactoryOzoneNativeBuffer::CreateGpuMemoryBuffer(
     gfx::GpuMemoryBuffer::Usage usage,
     int client_id,
     gfx::PluginWindowHandle surface_handle) {
+  DCHECK(thread_checker_.CalledOnValidThread());
   scoped_refptr<NativePixmap> pixmap =
       SurfaceFactoryOzone::GetInstance()->CreateNativePixmap(
           surface_handle, size, GetOzoneFormatFor(format),
@@ -147,7 +148,6 @@ bool GpuMemoryBufferFactoryOzoneNativeBuffer::CreateGpuMemoryBuffer(
                << size.height() << " format " << format << ", usage " << usage;
     return false;
   }
-  base::AutoLock lock(native_pixmap_map_lock_);
   native_pixmap_map_[GetIndex(id, client_id)] = pixmap;
   return true;
 }
@@ -155,7 +155,7 @@ bool GpuMemoryBufferFactoryOzoneNativeBuffer::CreateGpuMemoryBuffer(
 void GpuMemoryBufferFactoryOzoneNativeBuffer::DestroyGpuMemoryBuffer(
     gfx::GpuMemoryBufferId id,
     int client_id) {
-  base::AutoLock lock(native_pixmap_map_lock_);
+  DCHECK(thread_checker_.CalledOnValidThread());
   native_pixmap_map_.erase(GetIndex(id, client_id));
 }
 
@@ -166,16 +166,13 @@ GpuMemoryBufferFactoryOzoneNativeBuffer::CreateImageForGpuMemoryBuffer(
     gfx::GpuMemoryBuffer::Format format,
     unsigned internalformat,
     int client_id) {
-  NativePixmap* pixmap = nullptr;
-  {
-    base::AutoLock lock(native_pixmap_map_lock_);
-    BufferToPixmapMap::iterator it =
-        native_pixmap_map_.find(GetIndex(id, client_id));
-    if (it == native_pixmap_map_.end()) {
-      return scoped_refptr<gfx::GLImage>();
-    }
-    pixmap = it->second.get();
+  DCHECK(thread_checker_.CalledOnValidThread());
+  BufferToPixmapMap::iterator it =
+      native_pixmap_map_.find(GetIndex(id, client_id));
+  if (it == native_pixmap_map_.end()) {
+    return scoped_refptr<gfx::GLImage>();
   }
+  NativePixmap* pixmap = it->second.get();
   return CreateImageForPixmap(pixmap, size, format, internalformat);
 }