Add support to extension_shell and ash_shell to use external V8 snapshot files.

content/shell/browser/shell_content_browser_client.cc

Index: content/shell/browser/shell_content_browser_client.cc
diff --git a/content/shell/browser/shell_content_browser_client.cc b/content/shell/browser/shell_content_browser_client.cc
index 90cc70cfd2a1e47d4c3096abfa2a8dc017a69b43..0f9c8d29c43b6ed9bb1dd020224451b7d178be80 100644
--- a/content/shell/browser/shell_content_browser_client.cc
+++ b/content/shell/browser/shell_content_browser_client.cc
@@ -353,21 +353,13 @@ void ShellContentBrowserClient::GetAdditionalMappedFilesForChildProcess(
     FileDescriptorInfo* mappings) {
 #if defined(V8_USE_EXTERNAL_STARTUP_DATA)
   if (v8_snapshot_fd_.get() == -1 && v8_natives_fd_.get() == -1) {
-    base::FilePath v8_data_path;
-    PathService::Get(gin::IsolateHolder::kV8SnapshotBasePathKey, &v8_data_path);
-    DCHECK(!v8_data_path.empty());
-
-    int file_flags = base::File::FLAG_OPEN | base::File::FLAG_READ;
-    base::FilePath v8_natives_data_path =
-        v8_data_path.AppendASCII(gin::IsolateHolder::kNativesFileName);
-    base::FilePath v8_snapshot_data_path =
-        v8_data_path.AppendASCII(gin::IsolateHolder::kSnapshotFileName);
-    base::File v8_natives_data_file(v8_natives_data_path, file_flags);
-    base::File v8_snapshot_data_file(v8_snapshot_data_path, file_flags);
-    DCHECK(v8_natives_data_file.IsValid());
-    DCHECK(v8_snapshot_data_file.IsValid());
-    v8_natives_fd_.reset(v8_natives_data_file.TakePlatformFile());
-    v8_snapshot_fd_.reset(v8_snapshot_data_file.TakePlatformFile());
+    int v8_natives_fd = -1;
+    int v8_snapshot_fd = -1;
+    if (gin::IsolateHolder::MapV8FilesForChildProcesses(&v8_natives_fd,
+                                                        &v8_snapshot_fd)) {
+      v8_natives_fd_.reset(v8_natives_fd);
+      v8_snapshot_fd_.reset(v8_snapshot_fd);
+    }
   }
   mappings->Share(kV8NativesDataDescriptor, v8_natives_fd_.get());
   mappings->Share(kV8SnapshotDataDescriptor, v8_snapshot_fd_.get());