Fix incldues to be flutter/shell rather than shell/ (flutter#21889)

Author: iskakaushik

shell/platform/android/external_view_embedder/external_view_embedder_unittests.cc

@@ -10,10 +10,10 @@
 #include "flutter/fml/raster_thread_merger.h"
 #include "flutter/fml/thread.h"
 #include "flutter/shell/platform/android/jni/jni_mock.h"
+#include "flutter/shell/platform/android/surface/android_surface.h"
 #include "flutter/shell/platform/android/surface/android_surface_mock.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
-#include "shell/platform/android/surface/android_surface.h"
 #include "third_party/skia/include/gpu/GrDirectContext.h"
 
 namespace flutter {

shell/platform/android/platform_view_android.cc

@@ -14,8 +14,8 @@
 #include "flutter/shell/platform/android/android_external_texture_gl.h"
 #include "flutter/shell/platform/android/android_surface_gl.h"
 #include "flutter/shell/platform/android/android_surface_software.h"
-#include "shell/platform/android/external_view_embedder/external_view_embedder.h"
-#include "shell/platform/android/surface/android_surface.h"
+#include "flutter/shell/platform/android/external_view_embedder/external_view_embedder.h"
+#include "flutter/shell/platform/android/surface/android_surface.h"
 
 #if SHELL_ENABLE_VULKAN
 #include "flutter/shell/platform/android/android_surface_vulkan.h"