Don't clear the forward history when replacing entries.

content/browser/frame_host/navigation_controller_impl_browsertest.cc

Index: content/browser/frame_host/navigation_controller_impl_browsertest.cc
diff --git a/content/browser/frame_host/navigation_controller_impl_browsertest.cc b/content/browser/frame_host/navigation_controller_impl_browsertest.cc
index ba4a49d1d4de3f05005e651f220a64d46afd8550..80b38051ef66d98e9c01038a9e985041ccf5b70e 100644
--- a/content/browser/frame_host/navigation_controller_impl_browsertest.cc
+++ b/content/browser/frame_host/navigation_controller_impl_browsertest.cc
@@ -186,10 +186,31 @@ IN_PROC_BROWSER_TEST_F(NavigationControllerBrowserTest,
   EXPECT_EQ(1, controller.GetEntryCount());
   EXPECT_EQ(1, RendererHistoryLength(shell()));
 
-  EXPECT_TRUE(NavigateToURLAndReplace(shell(), GURL("data:text/html,page2")));
+  EXPECT_TRUE(NavigateToURLAndReplace(shell(), GURL("data:text/html,page1a")));
   EXPECT_EQ(1, controller.GetEntryCount());
   EXPECT_EQ(1, RendererHistoryLength(shell()));
 
+  // Now create two more entries and go back, to test replacing an entry without
+  // pruning the forward history.
+  EXPECT_TRUE(NavigateToURL(shell(), GURL("data:text/html,page2")));
+  EXPECT_EQ(2, controller.GetEntryCount());
+  EXPECT_EQ(2, RendererHistoryLength(shell()));
+
+  EXPECT_TRUE(NavigateToURL(shell(), GURL("data:text/html,page3")));
+  EXPECT_EQ(3, controller.GetEntryCount());
+  EXPECT_EQ(3, RendererHistoryLength(shell()));
+
+  controller.GoBack();
+  EXPECT_TRUE(WaitForLoadStop(shell()->web_contents()));
+  controller.GoBack();
+  EXPECT_TRUE(WaitForLoadStop(shell()->web_contents()));
+  EXPECT_TRUE(controller.CanGoForward());
+
+  EXPECT_TRUE(NavigateToURLAndReplace(shell(), GURL("data:text/html,page1b")));
+  EXPECT_EQ(3, controller.GetEntryCount());
+  EXPECT_EQ(3, RendererHistoryLength(shell()));
+  EXPECT_TRUE(controller.CanGoForward());
+
   // Note that there's no way to access the renderer's notion of the history
   // offset via JavaScript. Checking just the history length, though, is enough;
   // if the replacement failed, there would be a new history entry and thus an