Revert of Linux: Disable DBus auto-launch (patchset #1 id:1 of https:…

…//codereview.chromium.org/2861163002/ )

Reason for revert:
Speculative revert -- the TSan bots have been reporting a data race when setting Envvars (in this case, appending to the python path to start a websocket server). The race appeared immediately after this patch landed, so it may be legitimate. Reverting this to see if it clears the failures up; if so, we'll probably just have to serialize the calls to setenv.

Filed crbug.com/719633 for this as well.

Original issue's description:
> Linux: Disable DBus auto-launch
>
> This is a workaround (ETA ~ 2-3 years) for libdbus not being multi-threading
> friendly and causing random hangs when running chrome outside of Linux
> desktop environments.
>
> Background:
> -----------
> Typically, Linux desktop environments set the DBUS_SESSION_BUS_ADDRESS
> environment variable. This variable allows the dbus client library to
> directly connect to the existing bus, which is started by the desktop
> environment or systemd.
> When this variable is missing, the dbus client library will fallback
> to auto-launch mode [1], which causes 4 nested fork() + exec() calls.
> Doing this has two problems: (i) slows down startup; (ii) can hang
> the browser if the fork() happens while another thread is in a malloc()
> (Chrome's tcmalloc has no at-fork handlers).
> This situation (no env variable) is very common in test scenarios
> (browsertests, chromedriver, etc).
>
> Change introduced by this CL:
> -----------------------------
> This CL sets the bus address env variable to "disabled:" if not set.
> This effectively shuts down the dbus auto-launch. If necessary, this
> behavior can be restored by setting, before launching chrome,
> DBUS_SESSION_BUS_ADDRESS="autolaunch:" .
> This workaround will be necessary until libdbus and gspawn are fixed
> to be multi-threading friendly [2,3] and that fix rolls into the
> various distributions.
> The change is introduced in the main embedder rather than in the
> google-chrome wrapper, as several binaries can be affected by this,
> for instance:
> - browser tests (http://crbug.com/693668)
> - chrome --headless
> - webdriver/selenium which seem to directly invoke "chrome"
>    see SeleniumHQ/docker-selenium#87
>
> [1] https://dbus.freedesktop.org/doc/dbus-launch.1.html
> [2] https://bugs.freedesktop.org/show_bug.cgi?id=100843
> [3] https://bugs.chromium.org/p/chromedriver/issues/detail?id=1699
>
> BUG=715658,695643,713947
> TEST=strace -ff -o trace chrome; grep dbus-launch trace*
>
> Review-Url: https://codereview.chromium.org/2861163002
> Cr-Commit-Position: refs/heads/master@{#469987}
> Committed: https://chromium.googlesource.com/chromium/src/+/8511820ec8280caacbd4f81f3ecd13b6c61681b0

[email protected],[email protected],[email protected],[email protected],[email protected]
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=715658,695643,713947

Review-Url: https://codereview.chromium.org/2869843003
Cr-Commit-Position: refs/heads/master@{#470059}

services/service_manager/embedder/main.cc

@@ -339,19 +339,6 @@ int Main(const MainParams& params) {
 #endif
   base::EnableTerminationOnOutOfMemory();
 
-#if defined(OS_LINUX)
-  // The various desktop environments set this environment variable that allows
-  // the dbus client library to connect directly to the bus. When this variable
-  // is not set (test environments like xvfb-run), the dbus client library will
-  // fall back to auto-launch mode. Auto-launch is dangerous as it can cause
-  // hangs (crbug.com/715658) . This one line disables the dbus auto-launch,
-  // by clobbering the DBUS_SESSION_BUS_ADDRESS env variable if not already set.
-  // The old auto-launch behavior, if needed, can be restored by setting
-  // DBUS_SESSION_BUS_ADDRESS="autolaunch:" before launching chrome.
-  const int kNoOverrideIfAlreadySet = 0;
-  setenv("DBUS_SESSION_BUS_ADDRESS", "disabled:", kNoOverrideIfAlreadySet);
-#endif
-
 #if defined(OS_WIN)
   base::win::RegisterInvalidParamHandler();
   ui::win::CreateATLModuleIfNeeded();