Add offset arguments to readPixels and compressedTex* per WebGL 2.0 spec.

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 1523 matching lines @@
                                  GLenum,
                                  GLint,
                                  GLint,
                                  GLint,
                                  ImageBitmap*,
                                  ExceptionState&);
   static const char* getTexImageFunctionName(TexImageFunctionID);
   IntRect sentinelEmptyRect();
   IntRect safeGetImageSize(Image*);
 
+  // Helper implementing readPixels for WebGL 1.0 and 2.0.
+  void readPixelsHelper(GLint x,
+                        GLint y,
+                        GLsizei width,
+                        GLsizei height,
+                        GLenum format,
+                        GLenum type,
+                        DOMArrayBufferView* pixels,
+                        GLuint offset);
+
  private:
   WebGLRenderingContextBase(HTMLCanvasElement*,
                             OffscreenCanvas*,
                             std::unique_ptr<WebGraphicsContext3DProvider>,
                             const CanvasContextCreationAttributes&,
                             unsigned);
   static std::unique_ptr<WebGraphicsContext3DProvider>
   createContextProviderInternal(HTMLCanvasElement*,
                                 ScriptState*,
                                 const CanvasContextCreationAttributes&,
@@ skipping 11 matching lines @@
                   context,
                   context->is3d(),
                   context.is3d());
 
 }  // namespace blink
 
 WTF_ALLOW_MOVE_INIT_AND_COMPARE_WITH_MEM_FUNCTIONS(
     blink::WebGLRenderingContextBase::TextureUnitState);
 
 #endif  // WebGLRenderingContextBase_h