すべてのシェーダーに適用されるグローバルな Texture プロパティーを設定します
Global properties are used if a shader needs them but the material does
not have them defined (for example, if the shader does not expose them
in Properties block).
Usually this is used if you have a set of custom shaders that all use
the same "global" texture (for example, custom diffuse-lighting cubemap).
Then you can set the global property from script and don't have to setup
the same texture in all materials.
関連項目: SetGlobalColor、SetGlobalFloat; Material クラス、ShaderLab ドキュメント.