Speculative fix for browser test MSAN flake

These browser tests launch a separate browser process to communicate
with. The browser process starts its own GPU process, and MSAN can hit
uninitialized values in some GL drivers on Chrome OS.

This ensures that the launched browser always uses swiftshader for GL to
avoid any such memory issues.

Fixed: 1131586
Change-Id: I012853118d390c4893933279930a64bba42028bd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2437017Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Ken Rockot <rockot@google.com>
Cr-Commit-Position: refs/heads/master@{#811769}

content/browser/launch_as_mojo_client_browsertest.cc

@@ -26,6 +26,10 @@
 #include "ui/ozone/public/ozone_switches.h"
 #endif
 
+#if defined(OS_CHROMEOS)
+#include "ui/gl/gl_switches.h"
+#endif
+
 namespace content {
 namespace {
 
@@ -79,6 +83,10 @@ class LaunchAsMojoClientBrowserTest : public ContentBrowserTest {
     const base::CommandLine& cmdline = *base::CommandLine::ForCurrentProcess();
     command_line.CopySwitchesFrom(cmdline, kSwitchesToCopy,
                                   base::size(kSwitchesToCopy));
+
+#if defined(OS_CHROMEOS)
+    command_line.AppendSwitchASCII(switches::kUseGL, "swiftshader");
+#endif
     return command_line;
   }