[features] Add kTopLevelAwait feature flag

The new feature flags enables top-level await for JavaScript modules.

TC39 proposal: https://github.com/tc39/proposal-top-level-await

Bug: 1022182, v8:9344
Change-Id: Icdba59e1b988c636b041d600e6c003bad2dd2f3a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2105375Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#750886}

content/public/common/content_features.h

@@ -137,6 +137,7 @@ CONTENT_EXPORT extern const base::Feature kStorageServiceSandbox;
 CONTENT_EXPORT extern const base::Feature kStrictOriginIsolation;
 CONTENT_EXPORT extern const base::Feature kSyntheticPointerActions;
 CONTENT_EXPORT extern const base::Feature kTimerThrottlingForHiddenFrames;
+CONTENT_EXPORT extern const base::Feature kTopLevelAwait;
 CONTENT_EXPORT extern const base::Feature kTouchpadAsyncPinchEvents;
 CONTENT_EXPORT extern const base::Feature kTouchpadOverscrollHistoryNavigation;
 CONTENT_EXPORT extern const base::Feature kTrustedDOMTypes;

content/renderer/render_process_impl.cc

@@ -37,6 +37,7 @@
 #include "content/public/common/content_switches.h"
 #include "content/public/renderer/content_renderer_client.h"
 #include "services/service_manager/embedder/switches.h"
+#include "third_party/blink/public/common/features.h"
 #include "third_party/blink/public/web/web_frame.h"
 #include "v8/include/v8.h"
 
@@ -140,6 +141,9 @@ RenderProcessImpl::RenderProcessImpl()
   SetV8FlagIfNotFeature(features::kWebAssemblySimd,
                         "--no-experimental-wasm-simd");
 
+  SetV8FlagIfFeature(blink::features::kTopLevelAwait,
+                     "--harmony-top-level-await");
+
   if (base::FeatureList::IsEnabled(features::kWebAssemblyThreads)) {
     constexpr char kFlags[] =
         "--harmony-sharedarraybuffer "

third_party/blink/common/features.cc

@@ -61,6 +61,10 @@ const base::Feature kDisplayLocking{"DisplayLocking",
 const base::Feature kJSONModules{"JSONModules",
                                  base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Enables top-level await in modules.
+const base::Feature kTopLevelAwait{"TopLevelAwait",
+                                   base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Enable LayoutNG.
 const base::Feature kLayoutNG{"LayoutNG", base::FEATURE_ENABLED_BY_DEFAULT};
 

third_party/blink/public/common/features.h

@@ -31,6 +31,7 @@ BLINK_COMMON_EXPORT extern const base::Feature kDisplayLocking;
 BLINK_COMMON_EXPORT extern const base::Feature
     kAssumeOverlapAfterFixedOrStickyPosition;
 BLINK_COMMON_EXPORT extern const base::Feature kJSONModules;
+BLINK_COMMON_EXPORT extern const base::Feature kTopLevelAwait;
 BLINK_COMMON_EXPORT extern const base::Feature kLayoutNG;
 BLINK_COMMON_EXPORT extern const base::Feature kMixedContentAutoupgrade;
 BLINK_COMMON_EXPORT extern const base::Feature kNavigationPredictor;