Change call-sites now that SkCanvas is not ref-counted

ui/surface/transport_dib_win.cc

Index: ui/surface/transport_dib_win.cc
diff --git a/ui/surface/transport_dib_win.cc b/ui/surface/transport_dib_win.cc
index 190065b9ded3acff714154ce7456a7362b218fb6..61f5a1b24295e639effc3650bed1965dd05d828f 100644
--- a/ui/surface/transport_dib_win.cc
+++ b/ui/surface/transport_dib_win.cc
@@ -58,8 +58,9 @@ bool TransportDIB::is_valid_handle(Handle dib) {
   return dib.IsValid();
 }
 
-SkCanvas* TransportDIB::GetPlatformCanvas(int w, int h,
-                                                      bool opaque) {
+std::unique_ptr<SkCanvas> TransportDIB::GetPlatformCanvas(int w,
+                                                          int h,
+                                                          bool opaque) {
   // This DIB already mapped the file into this process, but PlatformCanvas
   // will map it again.
   DCHECK(!memory()) << "Mapped file twice in the same process.";
@@ -67,7 +68,7 @@ SkCanvas* TransportDIB::GetPlatformCanvas(int w, int h,
   // We can't check the canvas size before mapping, but it's safe because
   // Windows will fail to map the section if the dimensions of the canvas
   // are too large.
-  SkCanvas* canvas = skia::CreatePlatformCanvas(
+  std::unique_ptr<SkCanvas> canvas = skia::CreatePlatformCanvas(
       w, h, opaque, shared_memory_.handle().GetHandle(),
       skia::RETURN_NULL_ON_FAILURE);