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

gin/isolate_holder.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "gin/public/isolate_holder.h"
 
 #include <stdlib.h>
 #include <string.h>
 
 #include "base/files/memory_mapped_file.h"
@@ skipping 176 matching lines @@
   base::MemoryMappedFile::Region snapshot_region =
       base::MemoryMappedFile::Region::kWholeFile;
   if (natives_size != 0 || natives_offset != 0) {
     snapshot_region =
         base::MemoryMappedFile::Region(snapshot_offset, snapshot_size);
   }
 
   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
 void IsolateHolder::GetV8ExternalSnapshotData(const char** natives_data_out,
                                               int* natives_size_out,
                                               const char** snapshot_data_out,
                                               int* snapshot_size_out) {
   if (!g_mapped_natives || !g_mapped_snapshot) {
     *natives_data_out = *snapshot_data_out = NULL;
     *natives_size_out = *snapshot_size_out = 0;
@@ skipping 84 matching lines @@
   base::MessageLoop::current()->AddTaskObserver(task_observer_.get());
 }
 
 void IsolateHolder::RemoveRunMicrotasksObserver() {
   DCHECK(task_observer_.get());
   base::MessageLoop::current()->RemoveTaskObserver(task_observer_.get());
   task_observer_.reset();
 }
 
 }  // namespace gin