Ensure trailing newline before EOF in C++ sources (#11489)

In generated text fixture location lookup code:
When the second argument to write_file() is a list, it is written one
item per line to the path specified by the first argument. This ensures
that we emit a trailing newline at EOF to comply with -Wnewline-eof.

Elsewhere:
Lack of a newline at EOF was undefined behaviour prior to C++11. The
Fuchsia tree sets -Wnewline-eof in its buildroot, so we plan to do the
same. This cleans up remaining first-party C++ sources that don't
include a trailing newline.

shell/platform/common/cpp/client_wrapper/include/flutter/json_type.h

@@ -23,4 +23,4 @@ using JsonValueType = rapidjson::Document;
 using JsonValueType = Json::Value;
 #endif
 
-#endif  // FLUTTER_SHELL_PLATFORM_COMMON_CPP_CLIENT_WRAPPER_INCLUDE_FLUTTER_JSON_TYPE_H_
\ No newline at end of file
+#endif  // FLUTTER_SHELL_PLATFORM_COMMON_CPP_CLIENT_WRAPPER_INCLUDE_FLUTTER_JSON_TYPE_H_

shell/platform/common/cpp/public/flutter_export.h

@@ -25,4 +25,4 @@
 
 #endif  // FLUTTER_DESKTOP_LIBRARY
 
-#endif  // FLUTTER_SHELL_PLATFORM_COMMON_CPP_PUBLIC_FLUTTER_EXPORT_H_
\ No newline at end of file
+#endif  // FLUTTER_SHELL_PLATFORM_COMMON_CPP_PUBLIC_FLUTTER_EXPORT_H_

shell/platform/darwin/macos/framework/Source/FlutterDartProject_Internal.h

@@ -35,4 +35,4 @@
 
 @end
 
-#endif  // SHELL_PLATFORM_DARWIN_MACOS_FRAMEWORK_SOURCE_FLUTTERDARTPROJECT_INTERNAL_H_
\ No newline at end of file
+#endif  // SHELL_PLATFORM_DARWIN_MACOS_FRAMEWORK_SOURCE_FLUTTERDARTPROJECT_INTERNAL_H_

testing/testing.gni

@@ -20,7 +20,10 @@ template("fixtures_location") {
   assert(defined(invoker.assets_dir), "The assets directory.")
 
   location_path = rebase_path(invoker.assets_dir)
-  location_source = "namespace flutter {namespace testing {const char* GetFixturesPath() {return \"$location_path\";}}}"
+
+  # Array of source lines. We use a list to ensure a trailing newline is
+  # emitted by write_file() to comply with -Wnewline-eof.
+  location_source = [ "namespace flutter {namespace testing {const char* GetFixturesPath() {return \"$location_path\";}}}" ]
   location_source_path = "$target_gen_dir/fixtures_location$target_name.cc"
 
   write_file(location_source_path, location_source)