polychrome: fix BrowserActionsBarBrowserTest tests

The process of fixing these tests uncovered a real bug in the Cocoa
BrowserActionsContainerView: it was always resizable even when highlighting.
This change:

1) Fixes that bug;
2) Adds an abstract CanBeResized test helper;
3) Implements that test helper for Cocoa and Views windows;
4) Marks the two drag & drop tests as Views-window-only, since the mechanics of
   drag & drop aren't exactly compatible between the two platforms.

Bug: 817408
Change-Id: I3a1316df05ff5aa1b3ae29c815fec6bac8062ad1
Reviewed-on: https://chromium-review.googlesource.com/963289
Commit-Queue: Elly Fong-Jones <[email protected]>
Reviewed-by: Robert Liao <[email protected]>
Cr-Commit-Position: refs/heads/master@{#543398}
diff --git a/chrome/browser/ui/extensions/browser_action_test_util.h b/chrome/browser/ui/extensions/browser_action_test_util.h
index 00c051c..f392ed8 100644
--- a/chrome/browser/ui/extensions/browser_action_test_util.h
+++ b/chrome/browser/ui/extensions/browser_action_test_util.h
@@ -104,6 +104,9 @@
   // Returns the maximum allowed size of an extension popup.
   virtual gfx::Size GetMaxPopupSize() = 0;
 
+  // Returns whether the browser action container can currently be resized.
+  virtual bool CanBeResized() = 0;
+
  protected:
   BrowserActionTestUtil() {}