Update {virtual,override} to follow C++11 style in ppapi.

The Google style guide states that only one of {virtual,override,final} should be used for each declaration, since override implies virtual and final implies both virtual and override.

This patch was manually generated using a regex and a text editor.

BUG=417463

Review URL: https://codereview.chromium.org/1097393007

Cr-Commit-Position: refs/heads/master@{#326505}

diff --git a/ppapi/proxy/plugin_resource_var.h b/ppapi/proxy/plugin_resource_var.h
index edfe47b4..461dbfd 100644
--- a/ppapi/proxy/plugin_resource_var.h
+++ b/ppapi/proxy/plugin_resource_var.h

@@ -22,13 +22,13 @@
   explicit PluginResourceVar(ppapi::Resource* resource);
 
   // ResourceVar override.
-  virtual PP_Resource GetPPResource() const override;
-  virtual bool IsPending() const override;
+  PP_Resource GetPPResource() const override;
+  bool IsPending() const override;
 
   scoped_refptr<ppapi::Resource> resource() const { return resource_; }
 
  protected:
-  virtual ~PluginResourceVar();
+  ~PluginResourceVar() override;
 
  private:
   // If NULL, this represents the PP_Resource 0.