gn: Allow users to set 'check_includes' in action_foreach().

Otherwise if someone tries to set it now it will get something like:

$ gn gen --args='os="android" cpu_arch="arm"' out_gn_android/Debug
ERROR at //build/config/android/rules.gni:49:22: Assignment had no
effect.
    check_includes = false
                         ^----
You set the variable "check_includes" here and it was unused before it went out of scope.
See //content/test/BUILD.gn:237:5: whence it was called.
generate_jni("jni") {
   ^--------------------

BUG=367595, 376000
TEST=see above
R=brettw@chromium.org

Review URL: https://codereview.chromium.org/885283006

Cr-Commit-Position: refs/heads/master@{#314794}

tools/gn/action_target_generator.cc

@@ -54,6 +54,9 @@ void ActionTargetGenerator::DoRun() {
   if (!FillDepfile())
     return;
 
+  if (!FillCheckIncludes())
+    return;
+
   if (!CheckOutputs())
     return;
 

tools/gn/binary_target_generator.cc

@@ -63,16 +63,6 @@ void BinaryTargetGenerator::DoRun() {
     return;
 }
 
-bool BinaryTargetGenerator::FillCheckIncludes() {
-  const Value* value = scope_->GetValue(variables::kCheckIncludes, true);
-  if (!value)
-    return true;
-  if (!value->VerifyTypeIs(Value::BOOLEAN, err_))
-    return false;
-  target_->set_check_includes(value->boolean_value());
-  return true;
-}
-
 bool BinaryTargetGenerator::FillCompleteStaticLib() {
   if (target_->output_type() == Target::STATIC_LIBRARY) {
     const Value* value = scope_->GetValue(variables::kCompleteStaticLib, true);

tools/gn/binary_target_generator.h

@@ -23,7 +23,6 @@ class BinaryTargetGenerator : public TargetGenerator {
   void DoRun() override;
 
  private:
-  bool FillCheckIncludes();
   bool FillCompleteStaticLib();
   bool FillOutputName();
   bool FillOutputExtension();

tools/gn/target_generator.cc

@@ -283,6 +283,16 @@ bool TargetGenerator::FillOutputs(bool allow_substitutions) {
   return true;
 }
 
+bool TargetGenerator::FillCheckIncludes() {
+  const Value* value = scope_->GetValue(variables::kCheckIncludes, true);
+  if (!value)
+    return true;
+  if (!value->VerifyTypeIs(Value::BOOLEAN, err_))
+    return false;
+  target_->set_check_includes(value->boolean_value());
+  return true;
+}
+
 bool TargetGenerator::EnsureSubstitutionIsInOutputDir(
     const SubstitutionPattern& pattern,
     const Value& original_value) {

tools/gn/target_generator.h

@@ -53,6 +53,7 @@ class TargetGenerator {
   bool FillInputs();
   bool FillConfigs();
   bool FillOutputs(bool allow_substitutions);
+  bool FillCheckIncludes();
 
   // Rrturns true if the given pattern will expand to a file in the output
   // directory. If not, returns false and sets the error, blaming the given