WebGL 2: add readPixels API to read pixels into pixel pack buffer

Source/modules/webgl/WebGL2RenderingContextBase.h

Index: Source/modules/webgl/WebGL2RenderingContextBase.h
diff --git a/Source/modules/webgl/WebGL2RenderingContextBase.h b/Source/modules/webgl/WebGL2RenderingContextBase.h
index 3922021b672bc23aae7d112b6b32b4b484e0724f..2c66ef15f04f751f91e239fbb1087c5e6d6c71c0 100644
--- a/Source/modules/webgl/WebGL2RenderingContextBase.h
+++ b/Source/modules/webgl/WebGL2RenderingContextBase.h
@@ -158,6 +158,9 @@ public:
     GLboolean isVertexArray(WebGLVertexArrayObject*);
     void bindVertexArray(WebGLVertexArrayObject*);
 
+    /* Reading */
+    void readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, long long offset);
+
     /* WebGLRenderingContextBase overrides */
     void initializeNewContext() override;
     void bindFramebuffer(GLenum target, WebGLFramebuffer*) override;
@@ -165,6 +168,7 @@ public:
     ScriptValue getParameter(ScriptState*, GLenum pname) override;
     ScriptValue getTexParameter(ScriptState*, GLenum target, GLenum pname) override;
     ScriptValue getFramebufferAttachmentParameter(ScriptState*, GLenum target, GLenum attachment, GLenum pname) override;
+    void readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, DOMArrayBufferView* pixels) override;
     void restoreCurrentFramebuffer() override;
 
     EAGERLY_FINALIZE();