Fix some override related warnings.

samples/particle_system/ParticleSystem.cpp

@@ -33,7 +33,7 @@ class ParticleSystemSample : public SampleApplication
     {
     }
 
-    virtual bool initialize()
+    bool initialize() override
     {
         const std::string vs = SHADER_SOURCE
         (
@@ -157,7 +157,7 @@ class ParticleSystemSample : public SampleApplication
         glUniform1f(mTimeLoc, mParticleTime);
     }
 
-    virtual void draw()
+    void draw() override
     {
         // Set the viewport
         glViewport(0, 0, getWindow()->getWidth(), getWindow()->getHeight());

src/libANGLE/renderer/gl/cgl/DisplayCGL.mm

@@ -33,7 +33,7 @@ class FunctionsGLCGL : public FunctionsGL
   public:
     FunctionsGLCGL(void *dylibHandle) : mDylibHandle(dylibHandle) {}
 
-    virtual ~FunctionsGLCGL() { dlclose(mDylibHandle); }
+    ~FunctionsGLCGL() override { dlclose(mDylibHandle); }
 
   private:
     void *loadProcAddress(const std::string &function) override

src/libANGLE/renderer/gl/glx/DisplayGLX.cpp

@@ -42,9 +42,7 @@ class FunctionsGLGLX : public FunctionsGL
     {
     }
 
-    virtual ~FunctionsGLGLX()
-    {
-    }
+    ~FunctionsGLGLX() override {}
 
   private:
     void *loadProcAddress(const std::string &function) override

src/libANGLE/renderer/gl/wgl/DisplayWGL.cpp

@@ -37,9 +37,7 @@ class FunctionsGLWindows : public FunctionsGL
         ASSERT(mGetProcAddressWGL);
     }
 
-    virtual ~FunctionsGLWindows()
-    {
-    }
+    ~FunctionsGLWindows() override {}
 
   private:
     void *loadProcAddress(const std::string &function) override