Emulate TEXTURE_IMMUTABLE_LEVELS on GL lower than 4.2

gpu/command_buffer/service/texture_manager.h

Index: gpu/command_buffer/service/texture_manager.h
diff --git a/gpu/command_buffer/service/texture_manager.h b/gpu/command_buffer/service/texture_manager.h
index 2485146677adff6954f45c6546ebc696ad37ed64..889712f97a2352fd7317c08ced2600d60b8521a7 100644
--- a/gpu/command_buffer/service/texture_manager.h
+++ b/gpu/command_buffer/service/texture_manager.h
@@ -246,6 +246,9 @@ class GPU_EXPORT Texture {
     return immutable_;
   }
 
+  // Return 0 if it's not immutable.
+  GLint GetImmutableLevels() const;
+
   // Get the cleared rectangle for a particular level. Returns an empty
   // rectangle if level does not exist.
   gfx::Rect GetLevelClearedRect(GLenum target, GLint level) const;