Always use Desktop GL 4.1 or less BindBufferRange behavior.

gpu/command_buffer/service/indexed_buffer_binding_host.h

 // Copyright (c) 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef GPU_COMMAND_BUFFER_SERVICE_INDEXED_BUFFER_BINDING_HOST_H_
 #define GPU_COMMAND_BUFFER_SERVICE_INDEXED_BUFFER_BINDING_HOST_H_
 
 #include <vector>
 
 #include "base/memory/ref_counted.h"
 #include "gpu/command_buffer/service/gl_utils.h"
 #include "gpu/gpu_export.h"
 
 namespace gpu {
 namespace gles2 {
 
 class Buffer;
 
 // This is a base class for indexed buffer bindings tracking.
 // TransformFeedback and Program should inherit from this base class,
 // for tracking indexed TRANSFORM_FEEDBACK_BUFFER / UNIFORM_BUFFER bindings.
 class GPU_EXPORT IndexedBufferBindingHost :
     public base::RefCounted<IndexedBufferBindingHost> {
  public:
-  // |needs_emulation| is set to true on Desktop GL 4.1 or lower.
+  // In theory |needs_emulation| needs to be true on Desktop GL 4.1 or lower.
+  // However, we set it to true everywhere, not to trust drivers to handle
+  // out-of-bounds buffer accesses.
   IndexedBufferBindingHost(uint32_t max_bindings, bool needs_emulation);
 
   // The following two functions do state update and call the underlying GL
   // function.  All validations have been done already and the GL function is
   // guaranteed to succeed.
   void DoBindBufferBase(GLenum target, GLuint index, Buffer* buffer);
   void DoBindBufferRange(
       GLenum target, GLuint index, Buffer* buffer, GLintptr offset,
       GLsizeiptr size);
 
@@ skipping 46 matching lines @@
     ~IndexedBufferBinding();
 
     bool operator==(const IndexedBufferBinding& other) const;
 
     void SetBindBufferBase(Buffer* _buffer);
     void SetBindBufferRange(
         Buffer* _buffer, GLintptr _offset, GLsizeiptr _size);
     void Reset();
   };
 
-  // This is called on Desktop GL lower than 4.2, where the range
+  // This is called when |needs_emulation_| is true, where the range
   // (offset + size) can't go beyond the buffer's size.
   static void DoAdjustedBindBufferRange(
       GLenum target, GLuint index, GLuint service_id, GLintptr offset,
       GLsizeiptr size, GLsizeiptr full_buffer_size);
 
   void UpdateMaxNonNullBindingIndex(size_t changed_index);
 
   std::vector<IndexedBufferBinding> buffer_bindings_;
 
   bool needs_emulation_;
 
   // This is used for optimization purpose in context switching.
   size_t max_non_null_binding_index_plus_one_;
 };
 
 }  // namespace gles2
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_SERVICE_INDEXED_BUFFER_BINDING_HOST_H_