cc: Partial tile update for one-copy raster.

cc/resources/resource_provider.cc

Index: cc/resources/resource_provider.cc
diff --git a/cc/resources/resource_provider.cc b/cc/resources/resource_provider.cc
index eb774fe10b3bd8d2ce217aa806d90a7158e3ca11..24fa2968f7a9c8776b5ef0aa2bfaf66fd8760284 100644
--- a/cc/resources/resource_provider.cc
+++ b/cc/resources/resource_provider.cc
@@ -1104,6 +1104,31 @@ ResourceProvider::ScopedWriteLockGpuMemoryBuffer::GetGpuMemoryBuffer() {
   return gpu_memory_buffer_;
 }
 
+ResourceProvider::ScopedReadLockGpuMemoryBuffer::ScopedReadLockGpuMemoryBuffer(
+    ResourceProvider* resource_provider,
+    ResourceProvider::ResourceId resource_id)
+    : resource_provider_(resource_provider),
+      resource_id_(resource_id),
+      gpu_memory_buffer_(nullptr) {
+  const Resource* resource = resource_provider->LockForRead(resource_id);
+  DCHECK_EQ(RESOURCE_TYPE_GL_TEXTURE, resource->type);
+  DCHECK(resource->allocated);
+  DCHECK(resource->image_id);
+  DCHECK(resource->gpu_memory_buffer);
+  gpu_memory_buffer_ = resource->gpu_memory_buffer;
+}
+
+ResourceProvider::ScopedReadLockGpuMemoryBuffer::
+    ~ScopedReadLockGpuMemoryBuffer() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  resource_provider_->UnlockForRead(resource_id_);
+}
+
+gfx::GpuMemoryBuffer*
+ResourceProvider::ScopedReadLockGpuMemoryBuffer::GetGpuMemoryBuffer() {
+  return gpu_memory_buffer_;
+}
+
 ResourceProvider::ScopedWriteLockGr::ScopedWriteLockGr(
     ResourceProvider* resource_provider,
     ResourceProvider::ResourceId resource_id)