Make the PDF viewer background color a property of the instance.

pdf/out_of_process_instance.h

Index: pdf/out_of_process_instance.h
diff --git a/pdf/out_of_process_instance.h b/pdf/out_of_process_instance.h
index eb304580fbb536300399243cb596322a04e16e22..9138d4c97a2c612b982d3f8eb0cdf8783ab75a65 100644
--- a/pdf/out_of_process_instance.h
+++ b/pdf/out_of_process_instance.h
@@ -136,6 +136,7 @@ class OutOfProcessInstance : public pp::Instance,
   void DocumentLoadProgress(uint32 available, uint32 doc_size) override;
   void FormTextFieldFocusChange(bool in_focus) override;
   bool IsPrintPreview() override;
+  uint32 GetBackgroundColor() override;
 
   // PreviewModeClient::Client implementation.
   void PreviewDocumentLoadComplete() override;
@@ -339,6 +340,9 @@ class OutOfProcessInstance : public pp::Instance,
   // zooming the plugin so that flickering doesn't occur while zooming.
   bool stop_scrolling_;
 
+  // The background color of the PDF viewer.
+  uint32 background_color_;
+
   // The callback for receiving the password from the page.
   scoped_ptr<pp::CompletionCallbackWithOutput<pp::Var> > password_callback_;
 };