enable fallback path

gpu/config/gpu_driver_bug_workaround_type.h

 // Copyright (c) 2013 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_CONFIG_GPU_DRIVER_BUG_WORKAROUND_TYPE_H_
 #define GPU_CONFIG_GPU_DRIVER_BUG_WORKAROUND_TYPE_H_
 
 #include <string>
 
 #include "gpu/gpu_export.h"
@@ skipping 173 matching lines @@
   GPU_OP(UNFOLD_SHORT_CIRCUIT_AS_TERNARY_OPERATION,          \
          unfold_short_circuit_as_ternary_operation)          \
   GPU_OP(UNPACK_ALIGNMENT_WORKAROUND_WITH_UNPACK_BUFFER,     \
          unpack_alignment_workaround_with_unpack_buffer)     \
   GPU_OP(UNPACK_IMAGE_HEIGHT_WORKAROUND_WITH_UNPACK_BUFFER,  \
          unpack_image_height_workaround_with_unpack_buffer)  \
   GPU_OP(UNPACK_OVERLAPPING_ROWS_SEPARATELY_UNPACK_BUFFER,   \
          unpack_overlapping_rows_separately_unpack_buffer)   \
   GPU_OP(USE_CLIENT_SIDE_ARRAYS_FOR_STREAM_BUFFERS,          \
          use_client_side_arrays_for_stream_buffers)          \
+  GPU_OP(USE_COPY_TEXTURE_FALLBACK_RGB5_A1,                  \
+         use_copy_texture_fallback_rgb5_a1)                  \
   GPU_OP(USE_INTERMEDIARY_FOR_COPY_TEXTURE_IMAGE,            \
          use_intermediary_for_copy_texture_image)            \
   GPU_OP(USE_NON_ZERO_SIZE_FOR_CLIENT_SIDE_STREAM_BUFFERS,   \
          use_non_zero_size_for_client_side_stream_buffers)   \
   GPU_OP(USE_SHADOWED_TEX_LEVEL_PARAMS,                      \
          use_shadowed_tex_level_params)                      \
   GPU_OP(USE_UNUSED_STANDARD_SHARED_BLOCKS,                  \
          use_unused_standard_shared_blocks)                  \
   GPU_OP(USE_VIRTUALIZED_GL_CONTEXTS,                        \
          use_virtualized_gl_contexts)                        \
@@ skipping 16 matching lines @@
 #undef GPU_OP
   NUMBER_OF_GPU_DRIVER_BUG_WORKAROUND_TYPES
 };
 
 GPU_EXPORT std::string GpuDriverBugWorkaroundTypeToString(
     GpuDriverBugWorkaroundType type);
 
 }  // namespace gpu
 
 #endif  // GPU_CONFIG_GPU_DRIVER_BUG_WORKAROUND_TYPE_H_