Allow ash-chrome to pass arguments to lacros-chrome.

Currently, when developing lacros-chrome on a ChromeOS device, passing
new arguments requires rebuilding ash-chrome. With this CL, the new flag
--lacros-chrome-additional-args can be used to pass flags from
ash-chrome directly to lacros-chrome. This means that developers can
modify /etc/chrome_dev.conf to pass flags to lacros-chrome without
rebuilding ash-chrome.

Bug: 1107936
Change-Id: I81d1d51451dce0e256c8c5d5d8e94016b4defa79
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2316812
Commit-Queue: Erik Chen <erikchen@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Auto-Submit: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791378}

chrome/browser/chromeos/crosapi/lacros_manager.cc

@@ -18,6 +18,7 @@
 #include "base/process/launch.h"
 #include "base/process/process_handle.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/strings/string_split.h"
 #include "base/task/task_traits.h"
 #include "base/task/thread_pool.h"
 #include "chrome/browser/chromeos/crosapi/ash_chrome_service_impl.h"
@@ -178,6 +179,16 @@ bool LacrosManager::Start() {
                                    "--lang=en-US",
                                    "--enable-crashpad"};
 
+  std::string additional_flags =
+      base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
+          chromeos::switches::kLacrosChromeAdditionalArgs);
+  std::vector<std::string> delimited_flags = base::SplitStringUsingSubstr(
+      additional_flags, "####", base::TRIM_WHITESPACE,
+      base::SPLIT_WANT_NONEMPTY);
+  for (const std::string& flag : delimited_flags) {
+    argv.push_back(flag);
+  }
+
   // We assume that if there's a custom chrome path, that this is a developer
   // and they want to enable logging.
   bool custom_chrome_path = base::CommandLine::ForCurrentProcess()->HasSwitch(

chromeos/constants/chromeos_switches.cc

@@ -413,6 +413,14 @@ const char kIgnoreUserProfileMappingForTests[] =
 // chrome://flags
 const char kKernelnextRestrictVMs[] = "kernelnext-restrict-vms";
 
+// If this switch is set, then ash-chrome will pass additional arguments when
+// launching lacros-chrome. The string '####' is used as a delimiter. Example:
+// --lacros-chrome-additional-args="--foo=5####--bar=/tmp/dir name". Will
+// result in two arguments passed to lacros-chrome:
+//   --foo=5
+//   --bar=/tmp/dir name
+const char kLacrosChromeAdditionalArgs[] = "lacros-chrome-additional-args";
+
 // If this switch is set, then ash-chrome will exec the lacros-chrome binary
 // from the indicated path rather than from component updater. Note that the
 // path should be to a directory that contains a binary named 'chrome'.

chromeos/constants/chromeos_switches.h

@@ -169,6 +169,8 @@ COMPONENT_EXPORT(CHROMEOS_CONSTANTS) extern const char kHomedir[];
 COMPONENT_EXPORT(CHROMEOS_CONSTANTS)
 extern const char kIgnoreUserProfileMappingForTests[];
 COMPONENT_EXPORT(CHROMEOS_CONSTANTS) extern const char kKernelnextRestrictVMs[];
+COMPONENT_EXPORT(CHROMEOS_CONSTANTS)
+extern const char kLacrosChromeAdditionalArgs[];
 COMPONENT_EXPORT(CHROMEOS_CONSTANTS) extern const char kLacrosChromePath[];
 COMPONENT_EXPORT(CHROMEOS_CONSTANTS) extern const char kLoginManager[];
 COMPONENT_EXPORT(CHROMEOS_CONSTANTS) extern const char kLoginProfile[];