Re-implement app overlap detection with new extent syntax.

chrome/common/extensions/extension_extent.h

Index: chrome/common/extensions/extension_extent.h
diff --git a/chrome/common/extensions/extension_extent.h b/chrome/common/extensions/extension_extent.h
index df8d02d020b668085fcd36f233d34d5f71981d50..a0117c5e324f510ac219b0f90a9fb0b6b133cabc 100644
--- a/chrome/common/extensions/extension_extent.h
+++ b/chrome/common/extensions/extension_extent.h
@@ -22,8 +22,12 @@ class ExtensionExtent {
   void AddPattern(const URLPattern& pattern) { patterns_.push_back(pattern); }
   void ClearPaths() { patterns_.clear(); }
 
+  // Test if the extent contains a URL.
   bool ContainsURL(const GURL& url) const;
 
+  // Returns true if there is a single URL that would be in two extents.
+  bool OverlapsWith(const ExtensionExtent& other) const;
+
  private:
   // The list of URL patterns that comprise the extent.
   PatternList patterns_;