Add an UMA metric to track whether chrome is running on a tablet.

chrome/browser/chrome_browser_main_win.cc

Index: chrome/browser/chrome_browser_main_win.cc
diff --git a/chrome/browser/chrome_browser_main_win.cc b/chrome/browser/chrome_browser_main_win.cc
index 3ff1f1ef44d8540b7648239d081c6a98c92f4de2..27e9fe1e57e5cc446043cc533a8a7598192eb0ad 100644
--- a/chrome/browser/chrome_browser_main_win.cc
+++ b/chrome/browser/chrome_browser_main_win.cc
@@ -14,11 +14,13 @@
 #include "base/files/file_path.h"
 #include "base/i18n/rtl.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/metrics/histogram.h"
 #include "base/path_service.h"
 #include "base/scoped_native_library.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/win/metro.h"
+#include "base/win/win_util.h"
 #include "base/win/windows_version.h"
 #include "base/win/wrapped_window_proc.h"
 #include "chrome/browser/browser_util_win.h"
@@ -245,6 +247,8 @@ void ChromeBrowserMainPartsWin::ShowMissingLocaleMessageBox() {
 void ChromeBrowserMainPartsWin::PostBrowserStart() {
   ChromeBrowserMainParts::PostBrowserStart();
 
+  UMA_HISTOGRAM_BOOLEAN("Windows.Tablet", base::win::IsTabletDevice());
+
   // Set up a task to verify installed modules in the current process. Use a
   // delay to reduce the impact on startup time.
   content::BrowserThread::GetMessageLoopProxyForThread(