Allow startup with missing V8 snapshot file.

ash/shell/content_client/shell_content_browser_client.cc

Index: ash/shell/content_client/shell_content_browser_client.cc
diff --git a/ash/shell/content_client/shell_content_browser_client.cc b/ash/shell/content_client/shell_content_browser_client.cc
index 51b0107d5ad9f1b8a532e3793655f9a506b1f193..518a6959ad5f7f71e927748ead15d556e990fd9c 100644
--- a/ash/shell/content_client/shell_content_browser_client.cc
+++ b/ash/shell/content_client/shell_content_browser_client.cc
@@ -51,8 +51,12 @@ void ShellContentBrowserClient::AppendExtraCommandLineSwitches(
   std::string process_type =
       command_line->GetSwitchValueASCII(switches::kProcessType);
   if (process_type != switches::kZygoteProcess) {
-    command_line->AppendSwitch(::switches::kV8NativesPassedByFD);
-    command_line->AppendSwitch(::switches::kV8SnapshotPassedByFD);
+    if (natives_fd_exists()) {

[rmcilroy, 2015/06/02 15:20:27]

Just DCHECK(natives_fd_exists() here since it should always be true from below
(and for all other ContentBrowserClient subclasses).

[Erik Corry Chromium.org, 2015/06/04 11:40:40]

Unfortunately this is also used for the GPU process, which does not have V8 and
so does not have the natives file open.

[rmcilroy, 2015/06/04 14:03:59]

I'm not sure this is to do with the gpu process - the ChildProcessLauncher
should be calling GetAdditionalMappedFilesForChildProcess no matter the process
type so this natives_fd_exists() should be true here even if the process in
question isn't going to use it.  The thing I'm worried about is that the process
launcher calls AppendExtraCommandLineSwitches before
GetAdditionalMappedFilesForChildProcess and therefore the first process launched
doesn't get the ::switches::kV8NativesPassedByFD in it's command line when it
should (which would cause it to fallback to loading directly from the
filesystem, which works on Linux but leads to issues during updates, and would
probably break on Android.

+      command_line->AppendSwitch(::switches::kV8NativesPassedByFD);
+    }
+    if (snapshot_fd_exists()) {
+      command_line->AppendSwitch(::switches::kV8SnapshotPassedByFD);
+    }
   }
 #endif  // V8_USE_EXTERNAL_STARTUP_DATA
 #endif  // OS_POSIX && !OS_MACOSX
@@ -64,7 +68,7 @@ void ShellContentBrowserClient::GetAdditionalMappedFilesForChildProcess(
     int child_process_id,
     content::FileDescriptorInfo* mappings) {
 #if defined(V8_USE_EXTERNAL_STARTUP_DATA)
-  if (v8_natives_fd_.get() == -1 || v8_snapshot_fd_.get() == -1) {
+  if (!natives_fd_exists()) {
     int v8_natives_fd = -1;
     int v8_snapshot_fd = -1;
     if (gin::V8Initializer::OpenV8FilesForChildProcesses(&v8_natives_fd,
@@ -73,7 +77,7 @@ void ShellContentBrowserClient::GetAdditionalMappedFilesForChildProcess(
       v8_snapshot_fd_.reset(v8_snapshot_fd);
     }
   }
-  DCHECK(v8_natives_fd_.get() != -1 && v8_snapshot_fd_.get() != -1);
+  DCHECK(natives_fd_exists());
   mappings->Share(kV8NativesDataDescriptor, v8_natives_fd_.get());
   mappings->Share(kV8SnapshotDataDescriptor, v8_snapshot_fd_.get());
 #endif  // V8_USE_EXTERNAL_STARTUP_DATA