Fix for the WebInputEventBuilderTest.TestMouseEventScale content_unittests failures on the DrMemory…

ui/gfx/display.cc

Index: ui/gfx/display.cc
diff --git a/ui/gfx/display.cc b/ui/gfx/display.cc
index c79dcea9ed1dcfedc7a2959cb67710a89a20841e..6bae399b4bfe4691dd947a808b326870d4fa410b 100644
--- a/ui/gfx/display.cc
+++ b/ui/gfx/display.cc
@@ -19,6 +19,16 @@
 namespace gfx {
 namespace {
 
+// This variable tracks whether the forced device scale factor switch needs to
+// be read from the command line, i.e. if it is set to -1 then the command line
+// is checked.
+int g_has_forced_device_scale_factor = -1;
+
+// This variable caches the forced device scale factor value which is read off
+// the command line. If the cache is invalidated by setting this variable to
+// -1.0, we read the forced device scale factor again.
+float g_forced_device_scale_factor = -1.0;
+
 bool HasForceDeviceScaleFactorImpl() {
   return base::CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kForceDeviceScaleFactor);
@@ -44,16 +54,22 @@ const int64 Display::kInvalidDisplayID = -1;
 
 // static
 float Display::GetForcedDeviceScaleFactor() {
-  static const float kForcedDeviceScaleFactor =

[sky, 2015/03/11 00:03:41]

UGH! Can we always look at the command line switch and avoid all this nonsense?

[ananta, 2015/03/11 00:06:52]

That would be great. Would this heavy traffic code path result in performance
issues caused by reading the command line each time?

-      GetForcedDeviceScaleFactorImpl();
-  return kForcedDeviceScaleFactor;
+  if (g_forced_device_scale_factor < 0)
+    g_forced_device_scale_factor = GetForcedDeviceScaleFactorImpl();
+  return GetForcedDeviceScaleFactorImpl();;
 }
 
 //static
 bool Display::HasForceDeviceScaleFactor() {
-  static const bool kHasForceDeviceScaleFactor =
-      HasForceDeviceScaleFactorImpl();
-  return kHasForceDeviceScaleFactor;
+  if (g_has_forced_device_scale_factor == -1)
+    g_has_forced_device_scale_factor = HasForceDeviceScaleFactorImpl();
+  return !!g_has_forced_device_scale_factor;
+}
+
+// static
+void Display::ResetForceDeviceScaleFactorForTesting() {
+  g_has_forced_device_scale_factor = -1;
+  g_forced_device_scale_factor = -1.0;
 }
 
 Display::Display()