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.cc b/chrome/browser/flag_descriptions.cc
index c5d76273..bcc762c 100644
--- a/chrome/browser/flag_descriptions.cc
+++ b/chrome/browser/flag_descriptions.cc
@@ -728,6 +728,11 @@
 const char kEnableWasmBaselineDescription[] =
     "Enables WebAssembly baseline compilation and tier up.";
 
+const char kEnableWasmThreadsName[] = "WebAssembly threads support.";
+const char kEnableWasmThreadsDescription[] =
+    "Enables support for the WebAssembly Threads proposal. Implies "
+    "#shared-array-buffer and #enable-webassembly.";
+
 const char kExpensiveBackgroundTimerThrottlingName[] =
     "Throttle expensive background timers";
 const char kExpensiveBackgroundTimerThrottlingDescription[] =