Implement base::win::IsMetroProcess.

base/win/metro.cc

Index: base/win/metro.cc
diff --git a/base/win/metro.cc b/base/win/metro.cc
index 81e3bdaabbfef42e218f8011ed8d7b14deb35970..cc92d52f970e78a80bd77e6d3b81de124296612a 100644
--- a/base/win/metro.cc
+++ b/base/win/metro.cc
@@ -15,6 +15,47 @@ HMODULE GetMetroModule() {
   return GetModuleHandleA("metro_driver.dll");
 }
 
+bool InMetroMode() {
+  enum ImmersiveState {
+    kImmersiveUnknown,
+    kImmersiveTrue,
+    kImmersiveFalse
+  };
+  typedef BOOL (WINAPI* IsImmersiveProcessFunc)(HANDLE process);
+
+  // Since the immersive state of a process can never change, we look it
+  // up once and then cache it here.
+  static ImmersiveState state = kImmersiveUnknown;
+
+  if (state == kImmersiveUnknown) {
+    // We didn't look it up yet. Note that the code below here is idempotent,
+    // so it doesn't matter if it races to assignment on multiple threads.
+    HMODULE user32 = ::GetModuleHandleA("user32.dll");
+    DCHECK(user32 != NULL);
+
+    IsImmersiveProcessFunc is_immersive_process =
+        reinterpret_cast<IsImmersiveProcessFunc>(
+            ::GetProcAddress(user32, "IsImmersiveProcess"));
+
+    if (is_immersive_process != NULL) {
+      if (is_immersive_process(::GetCurrentProcess())) {
+        DCHECK(GetMetroModule() != NULL);

[Sigurður Ásgeirsson, 2012/06/18 13:54:15]

This assert is apparently firing inside the renderers, I don't understand why
that would be happening (about to debug), but presumably we want the same answer
to the "InMetroMode" question in renders and browsers?

+
+        state = kImmersiveTrue;
+      } else {
+        state = kImmersiveFalse;
+      }
+    } else {
+      // No "IsImmersiveProcess" export on user32.dll, so we're pre-windows8
+      // and therefore not immersive.
+      state = kImmersiveFalse;
+    }
+  }
+  DCHECK_NE(kImmersiveUnknown, state);
+
+  return state == kImmersiveTrue;
+}
+
 wchar_t* LocalAllocAndCopyString(const string16& src) {
   size_t dest_size = (src.length() + 1) * sizeof(wchar_t);
   wchar_t* dest = reinterpret_cast<wchar_t*>(LocalAlloc(LPTR, dest_size));