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

content/renderer/pepper/pepper_plugin_instance_impl.cc

Index: content/renderer/pepper/pepper_plugin_instance_impl.cc
diff --git a/content/renderer/pepper/pepper_plugin_instance_impl.cc b/content/renderer/pepper/pepper_plugin_instance_impl.cc
index ac4b7931a7e7bff680542828fa28c08942b960a5..6254e040d1152557af19e959bd659b5214c1ac0f 100644
--- a/content/renderer/pepper/pepper_plugin_instance_impl.cc
+++ b/content/renderer/pepper/pepper_plugin_instance_impl.cc
@@ -1798,7 +1798,7 @@
   if (!num_pages)
     return 0;
   current_print_settings_ = print_settings;
-  canvas_ = nullptr;
+  canvas_.reset();
   ranges_.clear();
   return num_pages;
 }
@@ -1817,7 +1817,7 @@
 #endif  // defined(OS_MACOSX)
   if (save_for_later) {
     ranges_.push_back(page_range);
-    canvas_ = canvas;
+    canvas_ = sk_ref_sp(canvas);
   } else {
     PrintPageHelper(&page_range, 1, canvas);
   }
@@ -1849,8 +1849,8 @@
   // Keep a reference on the stack. See NOTE above.
   scoped_refptr<PepperPluginInstanceImpl> ref(this);
   if (!ranges_.empty())
-    PrintPageHelper(&(ranges_.front()), ranges_.size(), canvas_);
-  canvas_ = nullptr;
+    PrintPageHelper(&(ranges_.front()), ranges_.size(), canvas_.get());
+  canvas_.reset();
   ranges_.clear();
 
   DCHECK(plugin_print_interface_);