Add flag to enable WebAssembly threads

WebAssembly threads implicitly enables SharedArrayBuffer
(--enable-shared-array-buffer) and structured cloning WebAssembly.Module
(--enable-webassembly).

Bug: 852756
Change-Id: I89d04cf08f1ff8cb777cf67f794d0f88049b6443
Reviewed-on: https://chromium-review.googlesource.com/1105558
Commit-Queue: Ben Smith <[email protected]>
Reviewed-by: Jochen Eisinger <[email protected]>
Cr-Commit-Position: refs/heads/master@{#568676}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 827b9f7c..0218c0f5 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -462,6 +462,9 @@
 extern const char kEnableWasmBaselineName[];
 extern const char kEnableWasmBaselineDescription[];
 
+extern const char kEnableWasmThreadsName[];
+extern const char kEnableWasmThreadsDescription[];
+
 extern const char kExpensiveBackgroundTimerThrottlingName[];
 extern const char kExpensiveBackgroundTimerThrottlingDescription[];