Let FromGlobalGflags take an explicit default.

New features and the code paths enabling them are often gated behind
flags; initially, the defaults have these code paths disabled, i.e., the
flags are off by default. That default value is statically defined in
the flag's definition and FromGlobalGflags uses that static default.

In order to change this when ramping up exposure to the new feature, we
need to override this. Here, we add a new version of FromGlobalGflags
that lets a default be explicitly specified, and change
BoolFromGlobalGflags (only) to match.

Author: 3405691582

base/cvd/cuttlefish/host/commands/assemble_cvd/flags/from_gflags.cc

@@ -39,10 +39,9 @@ Result<std::string> ParseString(const std::string& value, const std::string&) {
 template <typename T>
 Result<std::vector<T>> FromGlobalGflags(
     const gflags::CommandLineFlagInfo& flag_info, const std::string& flag_name,
+    T default_value,
     std::function<Result<T>(const std::string& value, const std::string& name)>
         parse_func) {
-  T default_value = CF_EXPECT(parse_func(flag_info.default_value, flag_name));
-
   std::vector<std::string> string_values =
       android::base::Split(flag_info.current_value, ",");
   std::vector<T> values(string_values.size());
@@ -57,6 +56,16 @@ Result<std::vector<T>> FromGlobalGflags(
   return std::move(values);
 }
 
+template <typename T>
+Result<std::vector<T>> FromGlobalGflags(
+    const gflags::CommandLineFlagInfo& flag_info, const std::string& flag_name,
+    std::function<Result<T>(const std::string& value, const std::string& name)>
+        parse_func) {
+  T default_value = CF_EXPECT(parse_func(flag_info.default_value, flag_name));
+  return std::move(FromGlobalGflags<T>(
+      flag_info, flag_name, default_value, parse_func));
+}
+
 }  // namespace
 
 Result<std::vector<bool>> BoolFromGlobalGflags(
@@ -65,6 +74,13 @@ Result<std::vector<bool>> BoolFromGlobalGflags(
   return CF_EXPECT(FromGlobalGflags<bool>(flag_info, flag_name, ParseBool));
 }
 
+Result<std::vector<bool>> BoolFromGlobalGflags(
+    const gflags::CommandLineFlagInfo& flag_info,
+    const std::string& flag_name, bool default_value) {
+  return CF_EXPECT(FromGlobalGflags<bool>(
+       flag_info, flag_name, default_value, ParseBool));
+}
+
 Result<std::vector<int>> IntFromGlobalGflags(
     const gflags::CommandLineFlagInfo& flag_info,
     const std::string& flag_name) {

base/cvd/cuttlefish/host/commands/assemble_cvd/flags/from_gflags.h

@@ -27,6 +27,8 @@ namespace cuttlefish {
 
 Result<std::vector<bool>> BoolFromGlobalGflags(
     const gflags::CommandLineFlagInfo& flag_info, const std::string& flag_name);
+Result<std::vector<bool>> BoolFromGlobalGflags(
+    const gflags::CommandLineFlagInfo& flag_info, const std::string& flag_name, bool default_value);
 Result<std::vector<int>> IntFromGlobalGflags(
     const gflags::CommandLineFlagInfo& flag_info, const std::string& flag_name);
 Result<std::vector<std::string>> StringFromGlobalGflags(