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 <binji@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568676}

chrome/browser/about_flags.cc

@@ -1373,6 +1373,9 @@ const FeatureEntry kFeatureEntries[] = {
     {"enable-webassembly-baseline", flag_descriptions::kEnableWasmBaselineName,
      flag_descriptions::kEnableWasmBaselineDescription, kOsAll,
      FEATURE_VALUE_TYPE(features::kWebAssemblyBaseline)},
+    {"enable-webassembly-threads", flag_descriptions::kEnableWasmThreadsName,
+     flag_descriptions::kEnableWasmThreadsDescription, kOsAll,
+     FEATURE_VALUE_TYPE(features::kWebAssemblyThreads)},
     {"shared-array-buffer", flag_descriptions::kEnableSharedArrayBufferName,
      flag_descriptions::kEnableSharedArrayBufferDescription, kOsAll,
      FEATURE_VALUE_TYPE(features::kSharedArrayBuffer)},

chrome/browser/flag_descriptions.cc

@@ -728,6 +728,11 @@ const char kEnableWasmBaselineName[] = "WebAssembly baseline compiler";
 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[] =

chrome/browser/flag_descriptions.h

@@ -462,6 +462,9 @@ extern const char kEnableWasmStreamingDescription[];
 extern const char kEnableWasmBaselineName[];
 extern const char kEnableWasmBaselineDescription[];
 
+extern const char kEnableWasmThreadsName[];
+extern const char kEnableWasmThreadsDescription[];
+
 extern const char kExpensiveBackgroundTimerThrottlingName[];
 extern const char kExpensiveBackgroundTimerThrottlingDescription[];
 

content/child/runtime_features.cc

@@ -121,7 +121,8 @@ void SetRuntimeFeaturesDefaultsAndUpdateFromArgs(
       base::FeatureList::IsEnabled(features::kWebAssemblyStreaming));
 
   WebRuntimeFeatures::EnableSharedArrayBuffer(
-      base::FeatureList::IsEnabled(features::kSharedArrayBuffer));
+      base::FeatureList::IsEnabled(features::kSharedArrayBuffer) ||
+      base::FeatureList::IsEnabled(features::kWebAssemblyThreads));
 
   if (command_line.HasSwitch(switches::kDisableSharedWorkers))
     WebRuntimeFeatures::EnableSharedWorker(false);

content/public/common/content_features.cc

@@ -470,6 +470,11 @@ const base::Feature kWebAssemblyStreaming{"WebAssemblyStreaming",
 const base::Feature kWebAssemblyBaseline{"WebAssemblyBaseline",
                                          base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Enable WebAssembly threads.
+// https://github.com/WebAssembly/threads
+const base::Feature kWebAssemblyThreads{"WebAssemblyThreads",
+                                        base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Enable WebAssembly trap handler.
 const base::Feature kWebAssemblyTrapHandler{"WebAssemblyTrapHandler",
                                             base::FEATURE_DISABLED_BY_DEFAULT};

content/public/common/content_features.h

@@ -113,6 +113,7 @@ CONTENT_EXPORT extern const base::Feature kVrWebInputEditing;
 CONTENT_EXPORT extern const base::Feature kWebAssembly;
 CONTENT_EXPORT extern const base::Feature kWebAssemblyStreaming;
 CONTENT_EXPORT extern const base::Feature kWebAssemblyBaseline;
+CONTENT_EXPORT extern const base::Feature kWebAssemblyThreads;
 CONTENT_EXPORT extern const base::Feature kWebAssemblyTrapHandler;
 CONTENT_EXPORT extern const base::Feature kWebAuth;
 CONTENT_EXPORT extern const base::Feature kWebAuthBle;

content/renderer/render_process_impl.cc

@@ -138,8 +138,6 @@ RenderProcessImpl::RenderProcessImpl(
                      "--harmony-import-meta");
   SetV8FlagIfFeature(features::kAsmJsToWebAssembly, "--validate-asm");
   SetV8FlagIfNotFeature(features::kAsmJsToWebAssembly, "--no-validate-asm");
-  SetV8FlagIfNotFeature(features::kWebAssembly,
-                        "--wasm-disable-structured-cloning");
 
   SetV8FlagIfFeature(features::kV8Orinoco, "--no-single-threaded-gc");
   SetV8FlagIfNotFeature(features::kV8Orinoco, "--single-threaded-gc");
@@ -150,10 +148,21 @@ RenderProcessImpl::RenderProcessImpl(
   SetV8FlagIfFeature(features::kWebAssemblyBaseline, "--wasm-tier-up");
   SetV8FlagIfNotFeature(features::kWebAssemblyBaseline, "--no-wasm-tier-up");
 
-  SetV8FlagIfFeature(features::kSharedArrayBuffer,
-                     "--harmony-sharedarraybuffer");
-  SetV8FlagIfNotFeature(features::kSharedArrayBuffer,
-                        "--no-harmony-sharedarraybuffer");
+  if (base::FeatureList::IsEnabled(features::kWebAssemblyThreads)) {
+    constexpr char kFlags[] =
+        "--harmony-sharedarraybuffer "
+        "--no-wasm-disable-structured-cloning "
+        "--experimental-wasm-threads";
+
+    v8::V8::SetFlagsFromString(kFlags, sizeof(kFlags));
+  } else {
+    SetV8FlagIfNotFeature(features::kWebAssembly,
+                          "--wasm-disable-structured-cloning");
+    SetV8FlagIfFeature(features::kSharedArrayBuffer,
+                       "--harmony-sharedarraybuffer");
+    SetV8FlagIfNotFeature(features::kSharedArrayBuffer,
+                          "--no-harmony-sharedarraybuffer");
+  }
 
   SetV8FlagIfNotFeature(features::kWebAssemblyTrapHandler,
                         "--no-wasm-trap-handler");

tools/metrics/histograms/enums.xml

@@ -27894,6 +27894,7 @@ from previous Chrome versions.
   <int value="118991027" label="enable-accelerated-fixed-root-background"/>
   <int value="119185738"
       label="OmniboxUIExperimentMaxAutocompleteMatches:disabled"/>
+  <int value="119309423" label="WebAssemblyThreads:disabled"/>
   <int value="120429808" label="disable-new-profile-management"/>
   <int value="121684313" label="QuickUnlockPin:enabled"/>
   <int value="121858954" label="enable-supervised-user-safesites"/>
@@ -28647,6 +28648,7 @@ from previous Chrome versions.
   <int value="1803465156" label="enable-zero-suggest-most-visited"/>
   <int value="1803470125" label="SyncUSSSessions:enabled"/>
   <int value="1809940714" label="SpeculativeLaunchServiceWorker:disabled"/>
+  <int value="1810311887" label="WebAssemblyThreads:enabled"/>
   <int value="1812368073" label="enable-new-app-list-mixer"/>
   <int value="1814671708" label="disable-password-manager-reauthentication"/>
   <int value="1816843861" label="ServiceWorkerServicification:enabled"/>