Guard against duplicate adds in PrerenderLinkManager.

chrome/browser/prerender/prerender_unittest.cc

Index: chrome/browser/prerender/prerender_unittest.cc
diff --git a/chrome/browser/prerender/prerender_unittest.cc b/chrome/browser/prerender/prerender_unittest.cc
index a8f56cbeb7d3f9ffdd6f683a96fd59874a2adcf9..6b345ada058f35a2a7ce2fda6435d77e6c733e14 100644
--- a/chrome/browser/prerender/prerender_unittest.cc
+++ b/chrome/browser/prerender/prerender_unittest.cc
@@ -316,6 +316,10 @@ class PrerenderTest : public testing::Test {
     return prerender_link_manager_->IsEmpty();
   }
 
+  size_t CountFromPrerenderLinkManager() {

[mmenke, 2013/02/14 16:38:36]

This function name is wrong, since it only counts running prerenders.

[gavinp, 2013/02/14 16:43:51]

Done.

+    return prerender_link_manager_->CountRunningPrerenders();

[mmenke, 2013/02/14 16:38:36]

Is this right?  What if we create a second prerender, but don't start running
it?  That would also be bad, no?

[gavinp, 2013/02/14 16:43:51]

Done.

+  }
+
   int last_prerender_id() const {
     return last_prerender_id_;
   }
@@ -394,6 +398,31 @@ TEST_F(PrerenderTest, DuplicateTest) {
   ASSERT_EQ(prerender_contents, prerender_manager()->FindAndUseEntry(url));
 }
 
+// Makes sure that we do not create two running prerender entries for the same
+// launcher and prerender id.
+TEST_F(PrerenderTest, DoubleAddTest) {
+  SetConcurrency(2);
+
+  GURL url("http://www.google.com/");
+  DummyPrerenderContents* prerender_contents =
+      prerender_manager()->CreateNextPrerenderContents(
+          url,
+          FINAL_STATUS_USED);
+  EXPECT_TRUE(AddSimplePrerender(url));
+  EXPECT_TRUE(prerender_contents->prerendering_has_started());
+  DCHECK_EQ(1u, CountFromPrerenderLinkManager());
+
+  GURL url2("http://www.notgoogle.com/");
+  prerender_link_manager()->OnAddPrerender(kDefaultChildId,
+                                           last_prerender_id(),
+                                           url, content::Referrer(),
+                                           kSize, kDefaultRenderViewRouteId);
+  // The second add had the same launcher and prerender_id as a running
+  // prerender, so it should have done nothing.
+  DCHECK_EQ(1u, CountFromPrerenderLinkManager());
+  ASSERT_EQ(prerender_contents, prerender_manager()->FindAndUseEntry(url));
+}
+
 // Ensure that we expire a prerendered page after the max. permitted time.
 TEST_F(PrerenderTest, ExpireTest) {
   GURL url("http://www.google.com/");