Command Buffer: read pixels into pixel pack buffer

gpu/command_buffer/client/gles2_implementation.cc

Index: gpu/command_buffer/client/gles2_implementation.cc
diff --git a/gpu/command_buffer/client/gles2_implementation.cc b/gpu/command_buffer/client/gles2_implementation.cc
index 208a08bd0e05b07209f37756baed96f702ae79b7..c2add507ad49919aa1c4ae52bc868fcac9ac9dcc 100644
--- a/gpu/command_buffer/client/gles2_implementation.cc
+++ b/gpu/command_buffer/client/gles2_implementation.cc
@@ -3485,10 +3485,10 @@ void GLES2Implementation::ReadPixels(
   }
 
   if (bound_pixel_pack_buffer_) {
-    // TODO(zmo): Need to handle the case of reading into a PIXEL_PACK_BUFFER
-    // in ES3. For now, generate a GL error.
-    SetGLError(GL_INVALID_OPERATION, "glReadPixels",
-               "ReadPixels to a pixel pack buffer isn't implemented");
+    GLuint offset = ToGLuint(pixels);
+    helper_->ReadPixels(
+        xoffset, yoffset, width, height, format, type, 0, offset, 0, 0, false);
+    CheckGLError();
     return;
   }