Add logic to ResourceProvider to correctly lock GpuMemoryBuffer Resources.

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 ae6edc35efb9b60511ab110c7dcfcd32762b5f67..38e39c3832598fa33ca90157bffdc39ec95ba35e 100644
--- a/cc/resources/resource_provider.cc
+++ b/cc/resources/resource_provider.cc
@@ -1042,6 +1042,27 @@ ResourceProvider::ScopedWriteLockSoftware::~ScopedWriteLockSoftware() {
   resource_provider_->UnlockForWrite(resource_);
 }
 
+ResourceProvider::ScopedReadLockGpuMemoryBuffer::ScopedReadLockGpuMemoryBuffer(
+    ResourceProvider* resource_provider,
+    ResourceId resource_id)
+    : resource_provider_(resource_provider),
+      resource_id_(resource_id),
+      resource_(resource_provider->LockForRead(resource_id)) {
+  DCHECK(IsGpuResourceType(resource_->type));

[ccameron, 2016/05/17 03:36:38]

This will need to create the GpuMemoryBuffer from the (not yet existing)
CreateFromClientId method added in https://codereview.chromium.org/1975023002/.

We already have the plumbing for the GpuMemoryBufferId, but I am still working
on plumbing the gpu_memory_buffer_factor_client_id through.

[erikchen, 2016/05/17 22:13:20]

N/A

+}
+
+ResourceProvider::ScopedReadLockGpuMemoryBuffer::
+    ~ScopedReadLockGpuMemoryBuffer() {
+  resource_provider_->UnlockForRead(resource_id_);
+}
+
+bool ResourceProvider::ScopedReadLockGpuMemoryBuffer::
+    IsInUseByMacOSWindowServer() const {
+  if (!resource_->gpu_memory_buffer)
+    return false;
+  return resource_->gpu_memory_buffer->IsInUseByMacOSWindowServer();
+}
+
 ResourceProvider::ScopedWriteLockGpuMemoryBuffer::
     ScopedWriteLockGpuMemoryBuffer(ResourceProvider* resource_provider,
                                    ResourceId resource_id)