Revert "WAR: temporarily disable partial repaints (sony#388)" (sony#401)

This reverts commit 820ee19.

Author: HidenoriMatsubayashi

src/flutter/shell/platform/linux_embedded/surface/elinux_egl_surface.cc

@@ -174,11 +174,6 @@ void ELinuxEGLSurface::PopulateExistingDamage(const intptr_t fbo_id,
       0, 0, static_cast<double>(width_px_), static_cast<double>(height_px_)};
   existing_damage->damage = existing_damage_map_[fbo_id];
 
-  // Temporarily disabled partial repaints due to
-  // https://github.com/sony/flutter-embedded-linux/issues/334. Once
-  // https://github.com/flutter/engine/pull/45611 was merged and propagated to
-  // the stable channel, this will be lifted up.
-#if 0
   if (age > 1) {
     --age;
     // join up to (age - 1) last rects from damage history
@@ -202,7 +197,6 @@ void ELinuxEGLSurface::PopulateExistingDamage(const intptr_t fbo_id,
       }
     }
   }
-#endif
 }
 
 // Auxiliary function used to transform a FlutterRect into the format that is