Add a feature flag for flushing the icache for the embedded blob

The V8FlushEmbeddedBlobICache flag will be used in Finch experiment.

Bug: chromium:889460
Change-Id: Iedec7b32e7272fd4df4d741b786c8a1391d89beb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2267158Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#785739}

gin/gin_features.cc

@@ -29,4 +29,8 @@ const base::Feature kV8ConcurrentInlining{"V8ConcurrentInlining",
 // Enable per-context marking worklists in V8 GC.
 const base::Feature kV8PerContextMarkingWorklist{
     "V8PerContextMarkingWorklist", base::FEATURE_DISABLED_BY_DEFAULT};
+
+// Enable flushing of the instruction cache for the embedded blob.
+const base::Feature kV8FlushEmbeddedBlobICache{
+    "kV8FlushEmbeddedBlobICache", base::FEATURE_DISABLED_BY_DEFAULT};
 }  // namespace features

gin/gin_features.h

@@ -16,6 +16,7 @@ GIN_EXPORT extern const base::Feature kV8OffThreadFinalization;
 GIN_EXPORT extern const base::Feature kV8LazyFeedbackAllocation;
 GIN_EXPORT extern const base::Feature kV8ConcurrentInlining;
 GIN_EXPORT extern const base::Feature kV8PerContextMarkingWorklist;
+GIN_EXPORT extern const base::Feature kV8FlushEmbeddedBlobICache;
 
 }  // namespace features
 

gin/v8_initializer.cc

@@ -240,6 +240,14 @@ void V8Initializer::Initialize(IsolateHolder::ScriptMode mode) {
                                sizeof(stress_per_context_marking_worklist) - 1);
   }
 
+  if (base::FeatureList::IsEnabled(features::kV8FlushEmbeddedBlobICache)) {
+    static const char experimental_flush_embedded_blob_icache[] =
+        "--experimental-flush-embedded-blob-icache";
+    v8::V8::SetFlagsFromString(
+        experimental_flush_embedded_blob_icache,
+        sizeof(experimental_flush_embedded_blob_icache) - 1);
+  }
+
   if (IsolateHolder::kStrictMode == mode) {
     static const char use_strict[] = "--use_strict";
     v8::V8::SetFlagsFromString(use_strict, sizeof(use_strict) - 1);