xvfb: set dpi to 96 (xvfb defaults to 100).

scripts/slave/xvfb.py

Index: scripts/slave/xvfb.py
diff --git a/scripts/slave/xvfb.py b/scripts/slave/xvfb.py
index 7d4977b63f44733f8be635ae46ac4310a8c8e4b4..f5f357764358527eb361fc23bf2d2f1b026f9a29 100644
--- a/scripts/slave/xvfb.py
+++ b/scripts/slave/xvfb.py
@@ -72,7 +72,8 @@ def StartVirtualX(slave_build_name, build_dir, with_wm=True, server_dir=None):
 
   # Start a virtual X server that we run the tests in.  This makes it so we can
   # run the tests even if we didn't start the tests from an X session.
-  proc = subprocess.Popen([cmd, display, '-screen', '0', '1024x768x24', '-ac'],
+  proc = subprocess.Popen([cmd, display, '-screen', '0', '1024x768x24', '-ac',
+                           '-dpi', '96'],

[pfeifer, 2015/04/24 14:59:52]

With HiDPI becoming more popular, it's conceivable that one would want to write
tests for different DPI settings.

Is it worth making dpi an extra parameter to StartVirtualX which defaults to 96
?

                           stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
   xvfb_pid_filename = _XvfbPidFilename(slave_build_name)
   open(xvfb_pid_filename, 'w').write(str(proc.pid))