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

gin/isolate_holder.cc

Index: gin/isolate_holder.cc
diff --git a/gin/isolate_holder.cc b/gin/isolate_holder.cc
index 317b5822bd8f47f773a0927d1a2b18ef6c2ebcb8..e3b5db0ed5923d4b4767dbd60649608a56e3d526 100644
--- a/gin/isolate_holder.cc
+++ b/gin/isolate_holder.cc
@@ -194,6 +194,25 @@ bool IsolateHolder::LoadV8SnapshotFd(int natives_fd,
   return MapV8Files(
       NULL, NULL, natives_fd, snapshot_fd, natives_region, snapshot_region);
 }
+
+// static
+bool IsolateHolder::MapV8FilesForChildProcesses(int* natives_fd_out,

[James Cook, 2015/03/18 23:20:06]

This function always returns true. Does it need a return value? Should it return
false if one of the DCHECK conditions fails?

[rmcilroy, 2015/03/19 14:41:39]

Yes, this is probably better. Also changed the if's to DCHECKS in the
ContentBrowerClients since we want to catch this failing early (rather than
after the child has already started).  

+                                                int* snapshot_fd_out) {
+  base::FilePath data_path;
+  PathService::Get(kV8SnapshotBasePathKey, &data_path);
+  DCHECK(!data_path.empty());
+
+  int file_flags = base::File::FLAG_OPEN | base::File::FLAG_READ;
+  base::FilePath natives_data_path = data_path.AppendASCII(kNativesFileName);
+  base::FilePath snapshot_data_path = data_path.AppendASCII(kSnapshotFileName);
+  base::File natives_data_file(natives_data_path, file_flags);
+  base::File snapshot_data_file(snapshot_data_path, file_flags);
+  DCHECK(natives_data_file.IsValid());
+  DCHECK(snapshot_data_file.IsValid());
+  *natives_fd_out = natives_data_file.TakePlatformFile();
+  *snapshot_fd_out = snapshot_data_file.TakePlatformFile();
+  return true;
+}
 #endif  // V8_USE_EXTERNAL_STARTUP_DATA
 
 //static