[content shell] Always use the osmesa driver for layout tests, and disable the gpu blacklist

content/shell/shell_main_delegate.cc

Index: content/shell/shell_main_delegate.cc
diff --git a/content/shell/shell_main_delegate.cc b/content/shell/shell_main_delegate.cc
index 97ad101dfcc338755a49c11b7189ffcde1b257bf..ea8a4844349608838047a15a71ffb6152985109c 100644
--- a/content/shell/shell_main_delegate.cc
+++ b/content/shell/shell_main_delegate.cc
@@ -19,6 +19,7 @@
 #include "net/cookies/cookie_monster.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/base/ui_base_paths.h"
+#include "ui/gl/gl_switches.h"
 
 #if defined(OS_ANDROID)
 #include "base/global_descriptors_posix.h"
@@ -93,6 +94,10 @@ bool ShellMainDelegate::BasicStartupComplete(int* exit_code) {
         switches::kAllowFileAccessFromFiles);
     CommandLine::ForCurrentProcess()->AppendSwitch(
         switches::kForceCompositingMode);
+    CommandLine::ForCurrentProcess()->AppendSwitchASCII(
+        switches::kUseGL, gfx::kGLImplementationOSMesaName);
+    CommandLine::ForCurrentProcess()->AppendSwitch(
+        switches::kIgnoreGpuBlacklist);
     net::CookieMonster::EnableFileScheme();
     if (!WebKitTestPlatformInitialize()) {
       if (exit_code)