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

gin/public/isolate_holder.h

Index: gin/public/isolate_holder.h
diff --git a/gin/public/isolate_holder.h b/gin/public/isolate_holder.h
index 7968b1df0ba3edd8a9978105b927a494ec4cb5ef..cce92b2b29623e935f51a481348d15d4d871adeb 100644
--- a/gin/public/isolate_holder.h
+++ b/gin/public/isolate_holder.h
@@ -6,6 +6,7 @@
 #define GIN_PUBLIC_ISOLATE_HOLDER_H_
 
 #include "base/basictypes.h"
+#include "base/files/file.h"
 #include "base/memory/scoped_ptr.h"
 #include "gin/gin_export.h"
 #include "v8/include/v8.h"
@@ -56,13 +57,26 @@ class GIN_EXPORT IsolateHolder {
   static const char kNativesFileName[];
   static const char kSnapshotFileName[];
 
+  // Load the V8 snapshot data from the given file descriptors. If offset and
+  // size are zero it will load the whole file, otherwise it will map and load
+  // the region of the file specified by offset and size. Returns true on
+  // success.

[James Cook, 2015/03/19 15:48:37]

Thanks for documenting the other methods!

   static bool LoadV8SnapshotFd(int natives_fd,
                                int64 natives_offset,
                                int64 natives_size,
                                int snapshot_fd,
                                int64 snapshot_offset,
                                int64 snapshot_size);
+
+  // Load the V8 snapshot data from the snapshot files. Returns true on success.
   static bool LoadV8Snapshot();
+
+  // Opens the V8 snapshot data files and returns open file descriptors to these
+  // files in |natives_fd_out| and |snapshot_fd_out|, which can be passed to
+  // child processes.
+  static bool OpenV8FilesForChildProcesses(base::PlatformFile* natives_fd_out,
+                                           base::PlatformFile* snapshot_fd_out);
+
 #endif  // V8_USE_EXTERNAL_STARTUP_DATA
   static void GetV8ExternalSnapshotData(const char** natives_data_out,
                                         int* natives_size_out,