Default to 1 when --force-device-scale-factor has an invalid value.

ui/gfx/display.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/display.h"
 
 #include <algorithm>
 
 #include "base/command_line.h"
 #include "base/logging.h"
@@ skipping 22 matching lines @@
   return base::CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kForceDeviceScaleFactor);
 }
 
 float GetForcedDeviceScaleFactorImpl() {
   double scale_in_double = 1.0;
   if (HasForceDeviceScaleFactorImpl()) {
     std::string value =
         base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
             switches::kForceDeviceScaleFactor);
-    if (!base::StringToDouble(value, &scale_in_double))
+    if (!base::StringToDouble(value, &scale_in_double)) {
       LOG(ERROR) << "Failed to parse the default device scale factor:" << value;
+      scale_in_double = 1.0;
+    }
   }
   return static_cast<float>(scale_in_double);
 }
 
 int64 internal_display_id_ = -1;
 
 }  // namespace
 
 const int64 Display::kInvalidDisplayID = -1;
 
@@ skipping 159 matching lines @@
   DCHECK_NE(kInvalidDisplayID, display_id);
   return HasInternalDisplay() && internal_display_id_ == display_id;
 }
 
 // static
 bool Display::HasInternalDisplay() {
   return internal_display_id_ != kInvalidDisplayID;
 }
 
 }  // namespace gfx