Enable AppContainer support for GPU process.

This CL adds the necessary support to the GPU process launcher to enable
the AppContainer sandbox as well as UMA metrics and a new entry in
chrome://flags.

Bug: 807249
Change-Id: I92d1f5ef224e09952b8615a79da639edc83692e7
Reviewed-on: https://chromium-review.googlesource.com/912868
Commit-Queue: James Forshaw <[email protected]>
Reviewed-by: Jesse Doherty <[email protected]>
Reviewed-by: Will Harris <[email protected]>
Reviewed-by: Zhenyao Mo <[email protected]>
Cr-Commit-Position: refs/heads/master@{#536690}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 745ce900..5164d579 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1444,6 +1444,9 @@
 extern const char kEnableDesktopIosPromotionsName[];
 extern const char kEnableDesktopIosPromotionsDescription[];
 
+extern const char kEnableGpuAppcontainerName[];
+extern const char kEnableGpuAppcontainerDescription[];
+
 extern const char kGdiTextPrinting[];
 extern const char kGdiTextPrintingDescription[];