gpu, cmaa: improve |do_copy| condition logic

gpu/command_buffer/service/framebuffer_manager.cc

Index: gpu/command_buffer/service/framebuffer_manager.cc
diff --git a/gpu/command_buffer/service/framebuffer_manager.cc b/gpu/command_buffer/service/framebuffer_manager.cc
index 0fd59c5fd6ba1dfb618709f97b1a8269481fd6d2..d86b4f406d34a5ec57ba36c01001cb928578dcd7 100644
--- a/gpu/command_buffer/service/framebuffer_manager.cc
+++ b/gpu/command_buffer/service/framebuffer_manager.cc
@@ -66,6 +66,7 @@ class RenderbufferAttachment
 
   bool IsTextureAttachment() const override { return false; }
   bool IsRenderbufferAttachment() const override { return true; }
+  bool IsTextureAttachmentImmutable() const override { return false; }
 
   bool IsTexture(TextureRef* /* texture */) const override { return false; }
 
@@ -205,6 +206,9 @@ class TextureAttachment
 
   bool IsTextureAttachment() const override { return true; }
   bool IsRenderbufferAttachment() const override { return false; }
+  bool IsTextureAttachmentImmutable() const override {
+    return texture_ref_->texture()->IsImmutable();
+  }
 
   bool IsTexture(TextureRef* texture) const override {
     return texture == texture_ref_.get();