Revert "gin: Set V8 context snapshot as a default snapshot"

This reverts commit 231de835.

Reason for revert: This change seems to break per-build bisects on Windows.

Command run:
python bisect_builds.py -o -a win64 -g 64.0.3282.24 -b 65.0.3294.0 -p S:\src\bisect\profile --use-local-cache

Result:
You are probably looking for a change made after 522661 (known good), but no later than 522662 (first known bad).
CHANGELOG URL:
The script might not always return single CL as suspect as some perf builds might get missing due to failure.
  https://chromium.googlesource.com/chromium/src/+log/bf8135d0bce64496b872062a07b427ddff825ec5..231de835ae50977881282c8c7fbbc2a93388d4b6

Original change's description:
> gin: Set V8 context snapshot as a default snapshot
> 
> Thanks to the change in V8 to make external reference table optional,
> we can always use v8_context_snapshot.bin on platforms where it is
> avaiable.
> 
> This CL sets the file as the default snapshot blob, and removes
> setting snapshot in Isolate::CreateParam.
> 
> 
> Bug: 764576, 789964
> Change-Id: I16654eef810efcd0103e9a29659f4616c61f790b
> Reviewed-on: https://chromium-review.googlesource.com/802654
> Commit-Queue: Hitoshi Yoshida <peria@chromium.org>
> Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
> Reviewed-by: Kentaro Hara <haraken@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#522662}

TBR=peria@chromium.org,rmcilroy@chromium.org,haraken@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 764576, 789964
Change-Id: Ibe8ddd99b86fd00c2c2586645350401896c49084
Reviewed-on: https://chromium-review.googlesource.com/827705
Commit-Queue: Robert Liao <robliao@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Robert Liao <robliao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524261}

gin/BUILD.gn

@@ -4,7 +4,6 @@
 
 import("//testing/test.gni")
 import("//v8/gni/v8.gni")
-import("//tools/v8_context_snapshot/v8_context_snapshot.gni")
 
 component("gin") {
   sources = [
@@ -74,9 +73,6 @@ component("gin") {
       "$root_out_dir/natives_blob.bin",
       "$root_out_dir/snapshot_blob.bin",
     ]
-    if (use_v8_context_snapshot) {
-      data += [ "$root_out_dir/v8_context_snapshot.bin" ]
-    }
   }
 
   defines = [ "GIN_IMPLEMENTATION" ]
@@ -93,10 +89,7 @@ component("gin") {
     libs = [ "CoreFoundation.framework" ]
   }
 
-  configs += [
-    "//tools/v8_context_snapshot:use_v8_context_snapshot",
-    "//v8:external_startup_data",
-  ]
+  configs += [ "//v8:external_startup_data" ]
 }
 
 executable("gin_shell") {
@@ -113,10 +106,7 @@ executable("gin_shell") {
     "//v8",
   ]
 
-  configs += [
-    "//tools/v8_context_snapshot:use_v8_context_snapshot",
-    "//v8:external_startup_data",
-  ]
+  configs += [ "//v8:external_startup_data" ]
 }
 
 source_set("gin_test") {
@@ -132,14 +122,10 @@ source_set("gin_test") {
   ]
   deps = [
     "//base/test:test_support",
-    "//tools/v8_context_snapshot",
     "//v8",
   ]
 
-  configs += [
-    "//tools/v8_context_snapshot:use_v8_context_snapshot",
-    "//v8:external_startup_data",
-  ]
+  configs += [ "//v8:external_startup_data" ]
 }
 
 test("gin_unittests") {

gin/isolate_holder.cc

@@ -38,12 +38,16 @@ IsolateHolder::IsolateHolder(
 IsolateHolder::IsolateHolder(
     scoped_refptr<base::SingleThreadTaskRunner> task_runner,
     AccessMode access_mode)
-    : IsolateHolder(std::move(task_runner), access_mode, kAllowAtomicsWait) {}
+    : IsolateHolder(std::move(task_runner),
+                    access_mode,
+                    kAllowAtomicsWait,
+                    nullptr) {}
 
 IsolateHolder::IsolateHolder(
     scoped_refptr<base::SingleThreadTaskRunner> task_runner,
     AccessMode access_mode,
-    AllowAtomicsWaitMode atomics_wait_mode)
+    AllowAtomicsWaitMode atomics_wait_mode,
+    v8::StartupData* startup_data)
     : access_mode_(access_mode) {
   v8::ArrayBuffer::Allocator* allocator = g_array_buffer_allocator;
   CHECK(allocator) << "You need to invoke gin::IsolateHolder::Initialize first";
@@ -56,6 +60,14 @@ IsolateHolder::IsolateHolder(
   params.array_buffer_allocator = allocator;
   params.allow_atomics_wait = atomics_wait_mode == kAllowAtomicsWait;
   params.external_references = g_reference_table;
+
+  if (startup_data) {
+    CHECK(g_reference_table);
+    V8Initializer::GetV8ContextSnapshotData(startup_data);
+    if (startup_data->data) {
+      params.snapshot_blob = startup_data;
+    }
+  }
   isolate_ = v8::Isolate::New(params);
 
   // TODO(ssid): Make sure the task runner is never null here, crbug.com/762723.

gin/public/isolate_holder.h

@@ -59,7 +59,8 @@ class GIN_EXPORT IsolateHolder {
                 AccessMode access_mode);
   IsolateHolder(scoped_refptr<base::SingleThreadTaskRunner> task_runner,
                 AccessMode access_mode,
-                AllowAtomicsWaitMode atomics_wait_mode);
+                AllowAtomicsWaitMode atomics_wait_mode,
+                v8::StartupData* startup_data);
 
   // This constructor is to create V8 snapshot for Blink.
   // Note this constructor calls isolate->Enter() internally.

gin/shell/gin_main.cc

@@ -72,10 +72,7 @@ int main(int argc, char** argv) {
 #ifdef V8_USE_EXTERNAL_STARTUP_DATA
   gin::V8Initializer::LoadV8Snapshot();
   gin::V8Initializer::LoadV8Natives();
-#ifdef USE_V8_CONTEXT_SNAPSHOT
-  gin::V8Initializer::LoadV8ContextSnapshot();
-#endif  // USE_V8_CONTEXT_SNAPSHOT
-#endif  // V8_USE_EXTERNAL_STARTUP_DATA
+#endif
 
   base::MessageLoop message_loop;
   base::TaskScheduler::CreateAndStartWithDefaultParams("gin");

gin/shell_runner_unittest.cc

@@ -32,9 +32,6 @@ TEST(RunnerTest, Run) {
   gin::V8Initializer::LoadV8Snapshot();
   gin::V8Initializer::LoadV8Natives();
 #endif
-#ifdef USE_V8_CONTEXT_SNAPSHOT
-  gin::V8Initializer::LoadV8ContextSnapshot();
-#endif
 
   gin::IsolateHolder::Initialize(gin::IsolateHolder::kStrictMode,
                                  gin::IsolateHolder::kStableV8Extras,

gin/test/v8_test.cc

@@ -24,10 +24,6 @@ void V8Test::SetUp() {
   gin::V8Initializer::LoadV8Snapshot();
   gin::V8Initializer::LoadV8Natives();
 #endif
-#ifdef USE_V8_CONTEXT_SNAPSHOT
-  gin::V8Initializer::LoadV8ContextSnapshot();
-#endif
-
   gin::IsolateHolder::Initialize(gin::IsolateHolder::kStrictMode,
                                  gin::IsolateHolder::kStableV8Extras,
                                  gin::ArrayBufferAllocator::SharedInstance());

gin/v8_initializer.cc

@@ -242,22 +242,16 @@ void V8Initializer::Initialize(IsolateHolder::ScriptMode mode,
 
 #if defined(V8_USE_EXTERNAL_STARTUP_DATA)
   v8::StartupData natives;
-  GetMappedFileData(g_mapped_natives, &natives);
+  natives.data = reinterpret_cast<const char*>(g_mapped_natives->data());
+  natives.raw_size = static_cast<int>(g_mapped_natives->length());
   v8::V8::SetNativesDataBlob(&natives);
 
-#if defined(USE_V8_CONTEXT_SNAPSHOT)
-  if (g_mapped_v8_context_snapshot) {
-    v8::StartupData snapshot{};
-    GetMappedFileData(g_mapped_v8_context_snapshot, &snapshot);
-    v8::V8::SetSnapshotDataBlob(&snapshot);
-  }
-#else
   if (g_mapped_snapshot) {
-    v8::StartupData snapshot{};
-    GetMappedFileData(g_mapped_snapshot, &snapshot);
+    v8::StartupData snapshot;
+    snapshot.data = reinterpret_cast<const char*>(g_mapped_snapshot->data());
+    snapshot.raw_size = static_cast<int>(g_mapped_snapshot->length());
     v8::V8::SetSnapshotDataBlob(&snapshot);
   }
-#endif  // USE_V8_CONTEXT_SNAPSHOT
 #endif  // V8_USE_EXTERNAL_STARTUP_DATA
 
   v8::V8::SetEntropySource(&GenerateEntropy);

third_party/WebKit/Source/platform/bindings/V8PerIsolateData.cpp

@@ -62,10 +62,14 @@ V8PerIsolateData::V8PerIsolateData(
     WebTaskRunner* task_runner,
     V8ContextSnapshotMode v8_context_snapshot_mode)
     : v8_context_snapshot_mode_(v8_context_snapshot_mode),
-      isolate_holder_(task_runner,
-                      gin::IsolateHolder::kSingleThread,
-                      IsMainThread() ? gin::IsolateHolder::kDisallowAtomicsWait
-                                     : gin::IsolateHolder::kAllowAtomicsWait),
+      isolate_holder_(
+          task_runner,
+          gin::IsolateHolder::kSingleThread,
+          IsMainThread() ? gin::IsolateHolder::kDisallowAtomicsWait
+                         : gin::IsolateHolder::kAllowAtomicsWait,
+          v8_context_snapshot_mode_ == V8ContextSnapshotMode::kUseSnapshot
+              ? &startup_data_
+              : nullptr),
       interface_template_map_for_v8_context_snapshot_(GetIsolate()),
       string_cache_(WTF::WrapUnique(new StringCache(GetIsolate()))),
       private_property_(V8PrivateProperty::Create()),
@@ -74,6 +78,13 @@ V8PerIsolateData::V8PerIsolateData(
       is_handling_recursion_level_error_(false),
       is_reporting_exception_(false),
       runtime_call_stats_(base::DefaultTickClock::GetInstance()) {
+  // If it fails to load the snapshot file, falls back to kDontUseSnapshot mode.
+  // TODO(peria): Remove this fallback routine.
+  if (v8_context_snapshot_mode_ == V8ContextSnapshotMode::kUseSnapshot &&
+      !startup_data_.data) {
+    v8_context_snapshot_mode_ = V8ContextSnapshotMode::kDontUseSnapshot;
+  }
+
   // FIXME: Remove once all v8::Isolate::GetCurrent() calls are gone.
   GetIsolate()->Enter();
   GetIsolate()->AddBeforeCallEnteredCallback(&BeforeCallEnteredCallback);