Add a Finch experiment V8HugeMaxOldGenerationSizefor V8 heap size increase

Increase max_old_space_size to 4 GB based on availability of physical memory.
The purpose of this finch is to support web apps that require more heap space
for their data sets

Bug:958974

Change-Id: I7f6bb9e69a306331242434cfc03acd68ad32333d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1592792Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Maggie Chen <magchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#656851}

gin/gin_features.cc

@@ -18,4 +18,8 @@ const base::Feature kV8FlushBytecode{"V8FlushBytecode",
 const base::Feature kV8MemoryReducerForSmallHeaps{
     "V8MemoryReducerForSmallHeaps", base::FEATURE_ENABLED_BY_DEFAULT};
 
+// Increase V8 heap size to 4GB if the physical memory is bigger than 16 GB.
+const base::Feature kV8HugeMaxOldGenerationSize{
+    "V8HugeMaxOldGenerationSize", base::FEATURE_DISABLED_BY_DEFAULT};
+
 }  // namespace features

gin/gin_features.h

@@ -13,6 +13,7 @@ namespace features {
 GIN_EXPORT extern const base::Feature kV8OptimizeJavascript;
 GIN_EXPORT extern const base::Feature kV8FlushBytecode;
 GIN_EXPORT extern const base::Feature kV8MemoryReducerForSmallHeaps;
+GIN_EXPORT extern const base::Feature kV8HugeMaxOldGenerationSize;
 
 }  // namespace features
 

gin/v8_initializer.cc

@@ -232,6 +232,13 @@ void V8Initializer::Initialize(IsolateHolder::ScriptMode mode) {
                                sizeof(no_memory_reducer) - 1);
   }
 
+  if (base::FeatureList::IsEnabled(features::kV8HugeMaxOldGenerationSize)) {
+    static const char huge_max_old_generation_size[] =
+        "--huge_max_old_generation_size";
+    v8::V8::SetFlagsFromString(huge_max_old_generation_size,
+                               sizeof(huge_max_old_generation_size) - 1);
+  }
+
   if (IsolateHolder::kStrictMode == mode) {
     static const char use_strict[] = "--use_strict";
     v8::V8::SetFlagsFromString(use_strict, sizeof(use_strict) - 1);

testing/variations/fieldtrial_testing_config.json

@@ -5443,6 +5443,25 @@
             ]
         }
     ],
+    "V8HugeMaxOldGenerationSize": [
+        {
+            "platforms": [
+                "android",
+                "chromeos",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "V8HugeMaxOldGenerationSize"
+                    ]
+                }
+            ]
+        }
+    ],
     "V8Ignition": [
         {
             "platforms": [