Add GL_ANGLE_pack_reverse_row_order to command buffer

gpu/command_buffer/client/gles2_implementation.h

Index: gpu/command_buffer/client/gles2_implementation.h
===================================================================
--- gpu/command_buffer/client/gles2_implementation.h	(revision 110991)
+++ gpu/command_buffer/client/gles2_implementation.h	(working copy)
@@ -202,6 +202,14 @@
   void FreeUnusedSharedMemory();
 
  private:
+
+  // Used to track whether an extension is available
+  enum ExtensionStatus {
+      kAvailableExtensionStatus,
+      kUnavailableExtensionStatus,
+      kUnknownExtensionStatus
+  };
+
   // Wraps RingBufferWrapper to provide aligned allocations.
   class AlignedRingBuffer : public RingBufferWrapper {
    public:
@@ -338,6 +346,9 @@
     return static_cast<T>(result_buffer_);
   }
 
+  // Lazily determines if GL_ANGLE_pack_reverse_row_order is available
+  bool IsAnglePackReverseRowOrderAvailable();
+
   // Gets the GLError through our wrapper.
   GLenum GetGLError();
 
@@ -432,6 +443,8 @@
   std::queue<int32> swap_buffers_tokens_;
   std::queue<int32> rate_limit_tokens_;
 
+  ExtensionStatus angle_pack_reverse_row_order_status;
+
   GLState gl_state_;
 
   // pack alignment as last set by glPixelStorei
@@ -443,6 +456,9 @@
   // unpack yflip as last set by glPixelstorei
   bool unpack_flip_y_;
 
+  // pack reverse row order as last set by glPixelstorei
+  bool pack_reverse_row_order_;
+
   scoped_array<TextureUnit> texture_units_;
 
   // 0 to gl_state_.max_combined_texture_image_units.