Add -Wnon-virtual-dtor and fix a warning.

build/common.gypi

@@ -32,6 +32,7 @@
             '-Wundef',
             '-Wwrite-strings',
             '-Wno-format-nonliteral',
+            '-Wnon-virtual-dtor',
         ],
     },
     'target_defaults':

src/libANGLE/renderer/gl/CompilerGL.h

@@ -22,7 +22,7 @@ class CompilerGL : public CompilerImpl
     ~CompilerGL() override {}
 
     gl::Error release() override { return gl::Error(GL_NO_ERROR); }
-    ShShaderOutput getTranslatorOutputType() const { return mTranslatorOutputType; }
+    ShShaderOutput getTranslatorOutputType() const override { return mTranslatorOutputType; }
 
   private:
     ShShaderOutput mTranslatorOutputType;