Implement --ozone-platform flag to select OzonePlatform implementation at runtime

ui/ozone/ozone_platform.cc

 // Copyright 2013 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 "base/command_line.h"
 #include "base/logging.h"
 #include "ui/ozone/ozone_platform.h"
+#include "ui/ozone/ozone_platform_list.h"
+#include "ui/ozone/ozone_switches.h"
 
 namespace ui {
 
+namespace {
+
+// Helper to construct an OzonePlatform by name using the platform list.
+OzonePlatform* CreatePlatform(const std::string& platform_name) {
+  // The first platform is the defualt.
+  if (platform_name == "default" && kOzonePlatformCount > 0)
+    return kOzonePlatforms[0].constructor();
+
+  // Otherwise, search for a matching platform in the list.
+  for (int i = 0; i < kOzonePlatformCount; ++i)
+    if (platform_name == kOzonePlatforms[i].name)
+      return kOzonePlatforms[i].constructor();
+
+  LOG(FATAL) << "Invalid ozone platform: " << platform_name;
+  return NULL;  // not reached
+}
+
+// Returns the name of the platform to use (value of --ozone-platform flag).
+std::string GetRequestedPlatform() {
+  if (!CommandLine::ForCurrentProcess()->HasSwitch(switches::kOzonePlatform))
+    return "default";
+  return CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
+      switches::kOzonePlatform);
+}
+
+}  // namespace
+
 OzonePlatform::OzonePlatform() {}
 
 OzonePlatform::~OzonePlatform() {
   gfx::SurfaceFactoryOzone::SetInstance(NULL);
   ui::EventFactoryOzone::SetInstance(NULL);
 }
 
 // static
 void OzonePlatform::Initialize() {
   if (instance_)
     return;
 
-  instance_ = CreateDefaultOzonePlatform();
+  instance_ = CreatePlatform(GetRequestedPlatform());
 
   // Inject ozone interfaces.
   gfx::SurfaceFactoryOzone::SetInstance(instance_->GetSurfaceFactoryOzone());
   ui::EventFactoryOzone::SetInstance(instance_->GetEventFactoryOzone());
 }
 
 // static
 OzonePlatform* OzonePlatform::instance_;
 
 }  // namespace ui