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..c596a9aca34201bcd6033526f6fd34546ad04fd1 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_HasForcedDeviceScaleFactor = -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_ForcedDeviceScaleFactor = -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 =
-      GetForcedDeviceScaleFactorImpl();
-  return kForcedDeviceScaleFactor;
+  if (g_ForcedDeviceScaleFactor < 0)

[scottmg, 2015/03/10 23:02:01]

I think it would be less complex to have 

  bool g_have_computed_scale_factor = false;

And then have the reset function set that back to false, rather than overloading
the values themselves.

[ananta, 2015/03/10 23:31:57]

Sadly that would be tricky. Given that we have two static values which need to
be invalidated on one flag. Leaving this as is and renamed the global variables
as per discussion.

+    g_ForcedDeviceScaleFactor = GetForcedDeviceScaleFactorImpl();
+  return g_ForcedDeviceScaleFactor;
 }
 
 //static
 bool Display::HasForceDeviceScaleFactor() {
-  static const bool kHasForceDeviceScaleFactor =
-      HasForceDeviceScaleFactorImpl();
-  return kHasForceDeviceScaleFactor;
+  if (g_HasForcedDeviceScaleFactor == -1)
+    g_HasForcedDeviceScaleFactor = HasForceDeviceScaleFactorImpl();
+  return !!g_HasForcedDeviceScaleFactor;
+}
+
+// static
+void Display::ResetForceDeviceScaleFactor() {
+  g_HasForcedDeviceScaleFactor = -1;
+  g_ForcedDeviceScaleFactor = -1.0;
 }
 
 Display::Display()