macviews: don't try to use zero-size modals

The Mac window system doesn't support zero-size windows, so it's important that
DialogTestBrowserWindow not impose a 0x0 maximum size on constrained dialogs.

This fixes a slew of constrained window tests, like PrintPreviewUIUnitTest.*
and PrintPreviewDialogControllerUnitTest.*.

TBR=sky@chromium.org

Bug: 832676
Change-Id: I0708d20ef7e16468af6e13980994d063e3b7e87a
Reviewed-on: https://chromium-review.googlesource.com/1148011Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577502}

chrome/test/base/dialog_test_browser_window.cc

@@ -4,6 +4,7 @@
 
 #include "chrome/test/base/dialog_test_browser_window.h"
 
+#include "build/build_config.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_list.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
@@ -52,6 +53,10 @@ gfx::Point DialogTestBrowserWindow::GetDialogPosition(const gfx::Size& size) {
 }
 
 gfx::Size DialogTestBrowserWindow::GetMaximumDialogSize() {
+#if defined(OS_MACOSX)
+  // Zero-size windows aren't allowed on Mac.
+  return gfx::Size(1, 1);
+#endif
   return gfx::Size();
 }