Convert defined(OS_XXX) to BUILDFLAG(IS_XXX) in libcef

See https://crbug.com/1234043 for background.

libcef/browser/alloy/alloy_browser_main.cc

@@ -41,7 +41,7 @@
 #include "third_party/widevine/cdm/buildflags.h"
 #include "ui/base/resource/resource_bundle.h"
 
-#if defined(OS_LINUX)
+#if BUILDFLAG(IS_LINUX)
 #include "ui/ozone/buildflags.h"
 #if defined(USE_AURA) && BUILDFLAG(OZONE_PLATFORM_X11)
 #include "ui/events/devices/x11/touch_factory_x11.h"
@@ -54,7 +54,7 @@
 #include "ui/views/widget/desktop_aura/desktop_screen.h"
 #include "ui/wm/core/wm_state.h"
 
-#if defined(OS_WIN)
+#if BUILDFLAG(IS_WIN)
 #include "chrome/browser/chrome_browser_main_win.h"
 #include "chrome/browser/win/parental_controls.h"
 #include "components/os_crypt/os_crypt.h"
@@ -62,7 +62,7 @@
 #endif  // defined(USE_AURA)
 
 #if defined(TOOLKIT_VIEWS)
-#if defined(OS_MAC)
+#if BUILDFLAG(IS_MAC)
 #include "chrome/browser/ui/views/chrome_layout_provider.h"
 #include "chrome/browser/ui/views/chrome_views_delegate.h"
 #else
@@ -70,11 +70,11 @@
 #endif
 #endif  // defined(TOOLKIT_VIEWS)
 
-#if defined(USE_AURA) && defined(OS_LINUX)
+#if defined(USE_AURA) && BUILDFLAG(IS_LINUX)
 #include "ui/base/ime/init/input_method_initializer.h"
 #endif
 
-#if defined(OS_LINUX)
+#if BUILDFLAG(IS_LINUX)
 #include "libcef/browser/printing/print_dialog_linux.h"
 #endif
 
@@ -95,7 +95,7 @@ AlloyBrowserMainParts::~AlloyBrowserMainParts() {
 }
 
 int AlloyBrowserMainParts::PreEarlyInitialization() {
-#if defined(USE_AURA) && defined(OS_LINUX)
+#if defined(USE_AURA) && BUILDFLAG(IS_LINUX)
   // TODO(linux): Consider using a real input method or
   // views::LinuxUI::SetInstance.
   ui::InitializeInputMethodForTesting();
@@ -113,7 +113,7 @@ void AlloyBrowserMainParts::ToolkitInitialized() {
 #endif  // defined(USE_AURA)
 
 #if defined(TOOLKIT_VIEWS)
-#if defined(OS_MAC)
+#if BUILDFLAG(IS_MAC)
   views_delegate_ = std::make_unique<ChromeViewsDelegate>();
   layout_provider_ = ChromeLayoutProvider::CreateLayoutProvider();
 #else
@@ -123,13 +123,13 @@ void AlloyBrowserMainParts::ToolkitInitialized() {
 }
 
 void AlloyBrowserMainParts::PreCreateMainMessageLoop() {
-#if defined(OS_LINUX)
+#if BUILDFLAG(IS_LINUX)
 #if defined(USE_AURA) && BUILDFLAG(OZONE_PLATFORM_X11)
   ui::TouchFactory::SetTouchDeviceListFromCommandLine();
 #endif
 #endif
 
-#if defined(OS_WIN)
+#if BUILDFLAG(IS_WIN)
   // Initialize the OSCrypt.
   PrefService* local_state = g_browser_process->local_state();
   DCHECK(local_state);
@@ -139,13 +139,13 @@ void AlloyBrowserMainParts::PreCreateMainMessageLoop() {
   // installer_util references strings that are normally compiled into
   // setup.exe.  In Chrome, these strings are in the locale files.
   ChromeBrowserMainPartsWin::SetupInstallerUtilStrings();
-#endif  // defined(OS_WIN)
+#endif  // BUILDFLAG(IS_WIN)
 
   media_router::ChromeMediaRouterFactory::DoPlatformInit();
 }
 
 void AlloyBrowserMainParts::PostCreateMainMessageLoop() {
-#if defined(OS_LINUX)
+#if BUILDFLAG(IS_LINUX)
   printing::PrintingContextLinux::SetCreatePrintDialogFunction(
       &CefPrintDialogLinux::CreatePrintDialog);
   printing::PrintingContextLinux::SetPdfPaperSizeFunction(
@@ -154,7 +154,7 @@ void AlloyBrowserMainParts::PostCreateMainMessageLoop() {
 }
 
 int AlloyBrowserMainParts::PreCreateThreads() {
-#if defined(OS_WIN)
+#if BUILDFLAG(IS_WIN)
   PlatformInitialize();
 #endif
 
@@ -211,7 +211,7 @@ int AlloyBrowserMainParts::PreMainMessageLoopRun() {
 
   CefDevToolsManagerDelegate::StartHttpHandler(browser_context);
 
-#if defined(OS_WIN)
+#if BUILDFLAG(IS_WIN)
   // Windows parental controls calls can be slow, so we do an early init here
   // that calculates this value off of the UI thread.
   InitializeWinParentalControls();
@@ -260,7 +260,7 @@ void AlloyBrowserMainParts::PostDestroyThreads() {
 
 #if defined(TOOLKIT_VIEWS)
   views_delegate_.reset();
-#if defined(OS_MAC)
+#if BUILDFLAG(IS_MAC)
   layout_provider_.reset();
 #endif
 #endif  // defined(TOOLKIT_VIEWS)