Remove needless build_settings.h includes.

input_file_manager.h is a popular header and build_settings.h
is slow to parse (mostly due to it including <functional>),
and the include isn't even needed.

Remove the include from settings.h and output_file.h too while here.

Change-Id: If2e0993267bb6ba2d4588e3ef44e305e51e64904
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/6644
Commit-Queue: Scott Graham <scottmg@chromium.org>
Reviewed-by: Scott Graham <scottmg@chromium.org>

src/gn/config_values_generator.cc

diff --git a/src/gn/config_values_generator.cc b/src/gn/config_values_generator.cc
index 918c6b1..e6c7c36 100644
--- a/src/gn/config_values_generator.cc
+++ b/src/gn/config_values_generator.cc
@@ -5,6 +5,7 @@
 #include "gn/config_values_generator.h"
 
 #include "base/strings/string_util.h"
+#include "gn/build_settings.h"
 #include "gn/config_values.h"
 #include "gn/scope.h"
 #include "gn/settings.h"

src/gn/functions.cc

diff --git a/src/gn/functions.cc b/src/gn/functions.cc
index 57f93eb..91723f5 100644
--- a/src/gn/functions.cc
+++ b/src/gn/functions.cc
@@ -11,6 +11,7 @@
 
 #include "base/environment.h"
 #include "base/strings/string_util.h"
+#include "gn/build_settings.h"
 #include "gn/config.h"
 #include "gn/config_values_generator.h"
 #include "gn/err.h"

src/gn/input_file_manager.h

diff --git a/src/gn/input_file_manager.h b/src/gn/input_file_manager.h
index 32a97c7..c3633e8 100644
--- a/src/gn/input_file_manager.h
+++ b/src/gn/input_file_manager.h
@@ -15,12 +15,12 @@
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
-#include "gn/build_settings.h"
 #include "gn/input_file.h"
 #include "gn/parse_tree.h"
 #include "gn/settings.h"
 #include "util/auto_reset_event.h"
 
+class BuildSettings;
 class Err;
 class LocationRange;
 class ParseNode;

src/gn/output_file.h

diff --git a/src/gn/output_file.h b/src/gn/output_file.h
index 543cf97..d8d69ff 100644
--- a/src/gn/output_file.h
+++ b/src/gn/output_file.h
@@ -9,8 +9,8 @@
 
 #include <string>
 
-#include "gn/build_settings.h"
-
+class BuildSettings;
+class SourceDir;
 class SourceFile;
 
 // A simple wrapper around a string that indicates the string is a path

src/gn/settings.h

diff --git a/src/gn/settings.h b/src/gn/settings.h
index e3b6ed2..1ae3d38 100644
--- a/src/gn/settings.h
+++ b/src/gn/settings.h
@@ -7,13 +7,14 @@
 
 #include "base/files/file_path.h"
 #include "base/macros.h"
-#include "gn/build_settings.h"
 #include "gn/import_manager.h"
 #include "gn/output_file.h"
 #include "gn/scope.h"
 #include "gn/source_dir.h"
 #include "gn/toolchain.h"
 
+class BuildSettings;
+
 // Holds the settings for one toolchain invocation. There will be one
 // Settings object for each toolchain type, each referring to the same
 // BuildSettings object for shared stuff.