Allow selection of utility sub type in utility-startup-dialog

This CL enhances the --utility-startup-dialog switch to now take an
optional service sub type, and displays the subtype when waiting
for the debugger, or showing the dialog.

`chrome --utility-startup-dialog` works as before, prompting/pausing
for every utility process.

`chrome --utility-startup-dialog=data_decoder.mojom.DataDecoderService`
only prompts for the data decoder service.

We check for the switch first then interrogate its value to limit
any impact on normal startup time.

This should make it easier to debug specific utility processes.

Tests: manual tested on Windows & Linux
Change-Id: I0195432a9f826697a87c687406a30dbdf1bfa378
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2892176
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Commit-Queue: Alex Gough <ajgo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#882668}

content/utility/utility_main.cc

@@ -103,8 +103,15 @@ int UtilityMain(const MainFunctionParams& parameters) {
   base::SingleThreadTaskExecutor main_thread_task_executor(message_pump_type);
   base::PlatformThread::SetName("CrUtilityMain");
 
-  if (parameters.command_line.HasSwitch(switches::kUtilityStartupDialog))
-    WaitForDebugger("Utility");
+  if (parameters.command_line.HasSwitch(switches::kUtilityStartupDialog)) {
+    auto dialog_match = parameters.command_line.GetSwitchValueASCII(
+        switches::kUtilityStartupDialog);
+    auto sub_type =
+        parameters.command_line.GetSwitchValueASCII(switches::kUtilitySubType);
+    if (dialog_match.empty() || dialog_match == sub_type) {
+      WaitForDebugger(sub_type.empty() ? "Utility" : sub_type);
+    }
+  }
 
 #if defined(OS_LINUX) || defined(OS_CHROMEOS)
   // Initializes the sandbox before any threads are created.

docs/linux/debugging.md

@@ -83,6 +83,10 @@ to debug the renderer code. Go to
 https://www.chromium.org/blink/getting-started-with-blink-debugging for more
 information on how this can be done.
 
+For utilities you can use `--utility-startup-dialog` to have all utilities
+prompt, or `--utility-startup-dialog=data_decoder.mojom.DataDecoderService`
+to debug only a particular service type.
+
 #### Choosing which renderers to debug
 
 If you are starting multiple renderers then the above means that multiple gdb's

docs/mac/debugging.md

@@ -173,7 +173,7 @@ these startup-dialog switches for the relevant process type:
 
 * `--renderer-startup-dialog`
 * `--utility-startup-dialog`
-* `--renderer-startup-dialog`
+* `--utility-startup-dialog=data_decoder.mojom.DataDecoderService`
 
 After the process launches, it will print a message like this to standard error: