[SE] Make Stream movable

Summary:
The example code makes it clear that this is a much better design
decision.

Reviewers: jlebar

Subscribers: jprice, parallel_libs-commits

Differential Revision: https://reviews.llvm.org/D24142

llvm-svn: 280397

parallel-libs/streamexecutor/examples/Example.cpp

@@ -121,13 +121,13 @@ int main() {
       getOrDie(Device->allocateDeviceMemory<float>(ArraySize));
 
   // Run operations on a stream.
-  std::unique_ptr<se::Stream> Stream = getOrDie(Device->createStream());
-  Stream->thenCopyH2D<float>(HostX, X)
+  se::Stream Stream = getOrDie(Device->createStream());
+  Stream.thenCopyH2D<float>(HostX, X)
       .thenCopyH2D<float>(HostY, Y)
       .thenLaunch(ArraySize, 1, *Kernel, A, X, Y)
       .thenCopyD2H<float>(X, HostX);
   // Wait for the stream to complete.
-  se::dieIfError(Stream->blockHostUntilDone());
+  se::dieIfError(Stream.blockHostUntilDone());
 
   // Process output data in HostX.
   std::vector<float> ExpectedX = {4, 47, 90, 133};