Make ScopedGetDC() CHECK fail if GetDC(NULL) returns NULL.

base/win/scoped_hdc.h

Index: base/win/scoped_hdc.h
===================================================================
--- base/win/scoped_hdc.h	(revision 140592)
+++ base/win/scoped_hdc.h	(working copy)
@@ -21,8 +21,15 @@
   explicit ScopedGetDC(HWND hwnd)
       : hwnd_(hwnd),
         hdc_(GetDC(hwnd)) {
-    DCHECK(!hwnd_ || IsWindow(hwnd_));
-    DCHECK(hdc_);
+    if (hwnd_) {
+      DCHECK(IsWindow(hwnd_));
+      DCHECK(hdc_);
+    } else {
+      // If GetDC(NULL) returns NULL, something really bad has happened, like
+      // GDI handle exhaustion.  In this case Chrome is going to behave badly no
+      // matter what, so we may as well just force a crash now.
+      CHECK(hdc_);
+    }
   }
 
   ~ScopedGetDC() {