[Search] expose constants, add fudge factor

The SearchAggregator exposes it's constants to add stability to
tests.

It also has a fudge factor which increaases the number of results
it requests from providers to better support pagination when using
client side filtering.

platform/search/src/services/SearchAggregator.js

@@ -31,8 +31,6 @@ define([
 ) {
     "use strict";
 
-    var DEFAULT_MAX_RESULTS = 100;
-
     /**
      * Aggregates multiple search providers as a singular search provider.
      * Search providers are expected to implement a `query` method which returns
@@ -53,6 +51,23 @@ define([
         this.providers = providers;
     }
 
+    /**
+     * If max results is not specified in query, use this as default.
+     */
+    SearchAggregator.prototype.DEFAULT_MAX_RESULTS = 100;
+
+    /**
+     * Because filtering isn't implemented inside each provider, the fudge
+     * factor is a multiplier on the number of results returned-- more results
+     * than requested will be fetched, and then will be fetched.  This helps
+     * provide more predictable pagination when large numbers of matches exist
+     * but very few matches match filters.
+     *
+     * If a provider level filter implementation is implemented in the future,
+     * remove this.
+     */
+    SearchAggregator.prototype.FUDGE_FACTOR = 5;
+
     /**
      * Sends a query to each of the providers. Returns a promise for
      *   a result object that has the format
@@ -79,13 +94,13 @@ define([
             resultPromises;
 
         if (!maxResults) {
-            maxResults = DEFAULT_MAX_RESULTS;
+            maxResults = this.DEFAULT_MAX_RESULTS;
         }
 
         resultPromises = this.providers.map(function (provider) {
             return provider.query(
                 inputText,
-                maxResults
+                maxResults * aggregator.FUDGE_FACTOR
             );
         });
 

platform/search/test/services/SearchAggregatorSpec.js

@@ -49,6 +49,13 @@ define([
             aggregator = new SearchAggregator($q, objectService, providers);
         });
 
+        it("has a fudge factor", function () {
+            expect(aggregator.FUDGE_FACTOR).toBe(5);
+        });
+
+        it("has default max results", function () {
+            expect(aggregator.DEFAULT_MAX_RESULTS).toBe(100);
+        });
 
         it("can order model results by score", function () {
             var modelResults = {
@@ -170,7 +177,11 @@ define([
             providers.push(provider);
 
             aggregator.query('find me', 123, 'filter');
-            expect(provider.query).toHaveBeenCalledWith('find me', 123);
+            expect(provider.query)
+                .toHaveBeenCalledWith(
+                    'find me',
+                    123 * aggregator.FUDGE_FACTOR
+                );
             expect($q.all).toHaveBeenCalledWith(['i prooomise!']);
         });
 
@@ -181,7 +192,10 @@ define([
                 );
             providers.push(provider);
             aggregator.query('find me');
-            expect(provider.query).toHaveBeenCalledWith('find me', 100);
+            expect(provider.query).toHaveBeenCalledWith(
+                'find me',
+                aggregator.DEFAULT_MAX_RESULTS * aggregator.FUDGE_FACTOR
+            );
         });
 
         it('can combine responses from multiple providers', function () {