Reland "Remove hang watching of deprecated BrowserThreads."

Partial reland... keep StartWatching() calls to try to isolate
the issue

This is a reland of 91c22dbf
Original change's description:
> Remove hang watching of deprecated BrowserThreads.
>
> This is a partial reland of https://chromium-review.googlesource.com/c/chromium/src/+/705775
>
> That CL caused issue 768886 (spike in hang reports). I suspect this
> was caused by a change in enum IDs rather than this change to the
> hang watching code and this CL will help narrow down the cause.
>
> R=asvitkine@chromium.org
>
> Bug: 689520,768886
> Change-Id: Id7bf1c7b5f5d34c4b1e7b1e71e9b015725695997
> Reviewed-on: https://chromium-review.googlesource.com/743846
> Commit-Queue: Gabriel Charette <gab@chromium.org>
> Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#512509}

Bug: 689520, 768886
Change-Id: I138fc4b33e6316496ff35e927b2cfb5246b53a6d

NOPRESUBMIT=TRUE (shuffling of code using deprecated BrowserThread IDs)

Change-Id: I138fc4b33e6316496ff35e927b2cfb5246b53a6d
Reviewed-on: https://chromium-review.googlesource.com/848355Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#526736}

chrome/browser/metrics/thread_watcher.cc

@@ -466,13 +466,11 @@ void ThreadWatcherList::ParseCommandLine(
     crash_on_hang_thread_names =
         command_line.GetSwitchValueASCII(switches::kCrashOnHangThreads);
   } else if (channel != version_info::Channel::STABLE) {
-    // Default to crashing the browser if UI or IO or FILE threads are not
-    // responsive except in stable channel.
-    crash_on_hang_thread_names = base::StringPrintf(
-        "UI:%d:%d,IO:%d:%d,FILE:%d:%d",
-        kLiveThreadsThreshold, crash_seconds,
-        kLiveThreadsThreshold, crash_seconds,
-        kLiveThreadsThreshold, crash_seconds * 5);
+    // Default to crashing the browser if UI or IO threads are not responsive
+    // except in stable channel.
+    crash_on_hang_thread_names =
+        base::StringPrintf("UI:%d:%d,IO:%d:%d", kLiveThreadsThreshold,
+                           crash_seconds, kLiveThreadsThreshold, crash_seconds);
   }
 
   ParseCommandLineCrashOnHangThreads(crash_on_hang_thread_names,
@@ -552,6 +550,7 @@ void ThreadWatcherList::InitializeAndStartWatching(
                 unresponsive_threshold, crash_on_hang_threads);
   StartWatching(BrowserThread::IO, "IO", kSleepTime, kUnresponsiveTime,
                 unresponsive_threshold, crash_on_hang_threads);
+  // TODO(gab): Stop watching deprecated BrowserThreads, crbug.com/768886.
   StartWatching(BrowserThread::DB, "DB", kSleepTime, kUnresponsiveTime,
                 unresponsive_threshold, crash_on_hang_threads);
   StartWatching(BrowserThread::FILE, "FILE", kSleepTime, kUnresponsiveTime,

chrome/browser/metrics/thread_watcher_report_hang.cc

@@ -50,36 +50,12 @@ NOINLINE void ThreadUnresponsive_UI() {
   ReportThreadHang();
 }
 
-NOINLINE void ThreadUnresponsive_DB() {
-  volatile int inhibit_comdat = __LINE__;
-  ALLOW_UNUSED_LOCAL(inhibit_comdat);
-  ReportThreadHang();
-}
-
-NOINLINE void ThreadUnresponsive_FILE() {
-  volatile int inhibit_comdat = __LINE__;
-  ALLOW_UNUSED_LOCAL(inhibit_comdat);
-  ReportThreadHang();
-}
-
-NOINLINE void ThreadUnresponsive_FILE_USER_BLOCKING() {
-  volatile int inhibit_comdat = __LINE__;
-  ALLOW_UNUSED_LOCAL(inhibit_comdat);
-  ReportThreadHang();
-}
-
 NOINLINE void ThreadUnresponsive_PROCESS_LAUNCHER() {
   volatile int inhibit_comdat = __LINE__;
   ALLOW_UNUSED_LOCAL(inhibit_comdat);
   ReportThreadHang();
 }
 
-NOINLINE void ThreadUnresponsive_CACHE() {
-  volatile int inhibit_comdat = __LINE__;
-  ALLOW_UNUSED_LOCAL(inhibit_comdat);
-  ReportThreadHang();
-}
-
 NOINLINE void ThreadUnresponsive_IO() {
   volatile int inhibit_comdat = __LINE__;
   ALLOW_UNUSED_LOCAL(inhibit_comdat);
@@ -91,19 +67,16 @@ NOINLINE void CrashBecauseThreadWasUnresponsive(
   switch (thread_id) {
     case content::BrowserThread::UI:
       return ThreadUnresponsive_UI();
-    case content::BrowserThread::DB:
-      return ThreadUnresponsive_DB();
-    case content::BrowserThread::FILE:
-      return ThreadUnresponsive_FILE();
-    case content::BrowserThread::FILE_USER_BLOCKING:
-      return ThreadUnresponsive_FILE_USER_BLOCKING();
     case content::BrowserThread::PROCESS_LAUNCHER:
       return ThreadUnresponsive_PROCESS_LAUNCHER();
-    case content::BrowserThread::CACHE:
-      return ThreadUnresponsive_CACHE();
     case content::BrowserThread::IO:
       return ThreadUnresponsive_IO();
     case content::BrowserThread::ID_COUNT:
+    // TODO(gab): Get rid of deprecated BrowserThread IDs.
+    case content::BrowserThread::DB:
+    case content::BrowserThread::FILE:
+    case content::BrowserThread::FILE_USER_BLOCKING:
+    case content::BrowserThread::CACHE:
       NOTREACHED();
       break;
   }