fix(dialog): log warning if doctype is missing

Logs a warning in the dialog service, if the doctype is missing. In such cases, the page is put into quirks mode, which causes the dialog to take up the entire height of the viewport, without much feedback regarding why. We can't really do much to work around the height issue in Material, however not adding a doctype isn't a good idea in general.

Fixes #2351.

Author: crisbeto

src/lib/dialog/dialog.ts

@@ -1,4 +1,4 @@
-import {Injector, ComponentRef, Injectable, Optional, SkipSelf} from '@angular/core';
+import {Injector, ComponentRef, Injectable, Optional, SkipSelf, isDevMode} from '@angular/core';
 import {Observable} from 'rxjs/Observable';
 import {Subject} from 'rxjs/Subject';
 
@@ -49,7 +49,15 @@ export class MdDialog {
   constructor(
       private _overlay: Overlay,
       private _injector: Injector,
-      @Optional() @SkipSelf() private _parentDialog: MdDialog) { }
+      @Optional() @SkipSelf() private _parentDialog: MdDialog) {
+
+    if (isDevMode() && typeof document !== 'undefined' && !document.doctype) {
+      console.warn(
+        'Current document does not have a doctype. This may cause ' +
+        'the Angular Material dialog not to behave as expected.'
+      );
+    }
+  }
 
   /**
    * Opens a modal dialog containing the given component.