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

Adds support to extension_shell and ash_shell to use external V8 snapshot files
in preparation for moving ChromeOS and ChromeCast to use this.

Re-factors the chrome_content_browser_client and
content/shell_content_browser_client to allow more reuse
of the code which opens the V8 external snapshot for child processes
by adding IsolateHolder::OpenV8FilesForChildProcesses.

This does not yet switch ChromeOS to use external V8 snapshot files -
this will be done in follow up CL https://codereview.chromium.org/1019123002.

BUG=421063

Review URL: https://codereview.chromium.org/1019483002

Cr-Commit-Position: refs/heads/master@{#323953}

3 files changed, 42 insertions, 1 deletions

diff --git a/ash/shell/DEPS b/ash/shell/DEPS
index 1108a45..2e87ae5 100644
--- a/ash/shell/DEPS
+++ b/ash/shell/DEPS
@@ -1,5 +1,6 @@
 include_rules = [
   "+content/public",
   "+content/shell",
+  "+gin",
   "+sandbox",
 ]
diff --git a/ash/shell/content_client/shell_content_browser_client.cc b/ash/shell/content_client/shell_content_browser_client.cc
index f778787..7f956ec 100644
--- a/ash/shell/content_client/shell_content_browser_client.cc
+++ b/ash/shell/content_client/shell_content_browser_client.cc
@@ -5,14 +5,21 @@
 #include "ash/shell/content_client/shell_content_browser_client.h"
 
 #include "ash/shell/content_client/shell_browser_main_parts.h"
+#include "content/public/common/content_descriptors.h"
 #include "content/shell/browser/shell_browser_context.h"
+#include "gin/v8_initializer.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 
 namespace ash {
 namespace shell {
 
 ShellContentBrowserClient::ShellContentBrowserClient()
-    : shell_browser_main_parts_(NULL) {
+    :
+#if defined(OS_POSIX) && !defined(OS_MACOSX)
+      v8_natives_fd_(-1),
+      v8_snapshot_fd_(-1),
+#endif  // OS_POSIX && !OS_MACOSX
+      shell_browser_main_parts_(nullptr) {
 }
 
 ShellContentBrowserClient::~ShellContentBrowserClient() {
@@ -34,6 +41,28 @@ net::URLRequestContextGetter* ShellContentBrowserClient::CreateRequestContext(
                                              request_interceptors.Pass());
 }
 
+#if defined(OS_POSIX) && !defined(OS_MACOSX)
+void ShellContentBrowserClient::GetAdditionalMappedFilesForChildProcess(
+    const base::CommandLine& command_line,
+    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) {
+    int v8_natives_fd = -1;
+    int v8_snapshot_fd = -1;
+    if (gin::V8Initializer::OpenV8FilesForChildProcesses(&v8_natives_fd,
+                                                         &v8_snapshot_fd)) {
+      v8_natives_fd_.reset(v8_natives_fd);
+      v8_snapshot_fd_.reset(v8_snapshot_fd);
+    }
+  }
+  DCHECK(v8_natives_fd_.get() != -1 && v8_snapshot_fd_.get() != -1);
+  mappings->Share(kV8NativesDataDescriptor, v8_natives_fd_.get());
+  mappings->Share(kV8SnapshotDataDescriptor, v8_snapshot_fd_.get());
+#endif  // V8_USE_EXTERNAL_STARTUP_DATA
+}
+#endif  // OS_POSIX && !OS_MACOSX
+
 content::ShellBrowserContext* ShellContentBrowserClient::browser_context() {
   return shell_browser_main_parts_->browser_context();
 }
diff --git a/ash/shell/content_client/shell_content_browser_client.h b/ash/shell/content_client/shell_content_browser_client.h
index 1a5eb44..df62338 100644
--- a/ash/shell/content_client/shell_content_browser_client.h
+++ b/ash/shell/content_client/shell_content_browser_client.h
@@ -33,10 +33,21 @@ class ShellContentBrowserClient : public content::ContentBrowserClient {
       content::BrowserContext* browser_context,
       content::ProtocolHandlerMap* protocol_handlers,
       content::URLRequestInterceptorScopedVector request_interceptors) override;
+#if defined(OS_POSIX) && !defined(OS_MACOSX)
+  void GetAdditionalMappedFilesForChildProcess(
+      const base::CommandLine& command_line,
+      int child_process_id,
+      content::FileDescriptorInfo* mappings) override;
+#endif
 
   content::ShellBrowserContext* browser_context();
 
  private:
+#if defined(OS_POSIX) && !defined(OS_MACOSX)
+  base::ScopedFD v8_natives_fd_;
+  base::ScopedFD v8_snapshot_fd_;
+#endif
+
   ShellBrowserMainParts* shell_browser_main_parts_;
 
   DISALLOW_COPY_AND_ASSIGN(ShellContentBrowserClient);