Query NaCl processes' GDB debug port on the correct thread.

chrome/browser/task_manager/sampling/task_group.cc

Index: chrome/browser/task_manager/sampling/task_group.cc
diff --git a/chrome/browser/task_manager/sampling/task_group.cc b/chrome/browser/task_manager/sampling/task_group.cc
index d7fab26f8d64944db4aa3da4f1b4d03a783e06c9..e31f0d1478840b3df3c3121067cea50bc938d5d2 100644
--- a/chrome/browser/task_manager/sampling/task_group.cc
+++ b/chrome/browser/task_manager/sampling/task_group.cc
@@ -90,7 +90,7 @@ TaskGroup::TaskGroup(
       user_peak_handles_(-1),
 #endif  // defined(OS_WIN)
 #if !defined(DISABLE_NACL)
-      nacl_debug_stub_port_(-1),
+      nacl_debug_stub_port_(nacl::kGdbDebugStubPortUnknown),

[afakhry, 2017/01/23 17:41:55]

While we are here, can you please revise the expectation of the shown text here:
https://cs.chromium.org/chromium/src/chrome/browser/ui/task_manager/task_mana...

Are we showing the correct text? nacl::kGdbDebugStubPortUnknown shows the text
"Unknown". nacl::kGdbDebugStubPortUnused shows the text N/A text "-". -2, which
we use when NaCl debugging is disabled, shows the text "Disabled".

Your change here doesn't change the behavior at all since
nacl::kGdbDebugStubPortUnknown == -1, but just to verify we're showing the right
meaningful thing.

[Wez, 2017/01/23 19:21:01]

Hmmm, GetNaClPortText() doesn't need the -2 case, since it'll only be called if
NaCl debug ports are enabled; I'll update the impl to remove -2. Unfortunately
the enabled flag is not available to DCHECK there.

That said, perhaps it would be cleaner to have the TaskGroup sampler code "know"
that NaCl debug ports are disabled, and return kDisabled, kUnknown, kUnused, or
a value, to simplify the table model implementation?

 #endif  // !defined(DISABLE_NACL)
       idle_wakeups_per_second_(-1),
 #if defined(OS_LINUX)
@@ -258,12 +258,15 @@ void TaskGroup::RefreshWindowsHandles() {
 }
 
 #if !defined(DISABLE_NACL)
+static int GetNaClDebugStubPort(int process_id) {

[afakhry, 2017/01/23 17:41:55]

Can you please add a DCHECK_CURRENTLY_ON(content::BrowserThread::IO); to make it
clear?

[Wez, 2017/01/23 19:21:02]

I'd prefer to express that via the name, since this is a static function sitting
alongside its only caller, so a DCHECK seems overkill.

+  return nacl::NaClBrowser::GetInstance()->GetProcessGdbDebugStubPort(
+      process_id);
+}
+
 void TaskGroup::RefreshNaClDebugStubPort(int child_process_unique_id) {
-  nacl::NaClBrowser* nacl_browser = nacl::NaClBrowser::GetInstance();
   content::BrowserThread::PostTaskAndReplyWithResult(
       content::BrowserThread::IO, FROM_HERE,
-      base::Bind(&nacl::NaClBrowser::GetProcessGdbDebugStubPort,
-                 base::Unretained(nacl_browser), child_process_unique_id),
+      base::Bind(&GetNaClDebugStubPort, child_process_unique_id),
       base::Bind(&TaskGroup::OnRefreshNaClDebugStubPortDone,
                  weak_ptr_factory_.GetWeakPtr()));
 }