Add null check to WebGLRenderingContextBase::contextGL().

third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.h

 /*
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 362 matching lines @@
         // Restore as soon as possible, but only when
         // the canvas is visible.
         Auto
     };
     void loseContext(LostContextMode) override;
     void forceLostContext(LostContextMode, AutoRecoveryMethod);
     void forceRestoreContext();
     void loseContextImpl(LostContextMode, AutoRecoveryMethod);
 
     WebGraphicsContext3D* webContext() const { return drawingBuffer()->context(); }
-    gpu::gles2::GLES2Interface* contextGL() const { return drawingBuffer()->contextGL(); }
+    gpu::gles2::GLES2Interface* contextGL() const
+    {
+        DrawingBuffer* d = drawingBuffer();
+        if (!d)
+            return nullptr;
+        return d->contextGL();
+    }
     WebGLContextGroup* contextGroup() const { return m_contextGroup.get(); }
     Extensions3DUtil* extensionsUtil();
 
     void reshape(int width, int height) override;
 
     void markLayerComposited() override;
     ImageData* paintRenderingResultsToImageData(SourceDrawingBuffer) override;
 
     void removeSharedObject(WebGLSharedObject*);
     void removeContextObject(WebGLContextObject*);
@@ skipping 676 matching lines @@
     CrossThreadWeakPersistentThisPointer<WebGLRenderingContextBase> createWeakThisPointer() { return CrossThreadWeakPersistentThisPointer<WebGLRenderingContextBase>(this); }
 };
 
 DEFINE_TYPE_CASTS(WebGLRenderingContextBase, CanvasRenderingContext, context, context->is3d(), context.is3d());
 
 } // namespace blink
 
 WTF_ALLOW_MOVE_INIT_AND_COMPARE_WITH_MEM_FUNCTIONS(blink::WebGLRenderingContextBase::TextureUnitState);
 
 #endif // WebGLRenderingContextBase_h