Show a warning message if the cache might not be cleared between runs.

chrome/common/extensions/docs/examples/extensions/benchmark/background.html

Index: chrome/common/extensions/docs/examples/extensions/benchmark/background.html
diff --git a/chrome/common/extensions/docs/examples/extensions/benchmark/background.html b/chrome/common/extensions/docs/examples/extensions/benchmark/background.html
index d7af961e0d16437c4b7b36cb8736d1a8d178a6ca..c560e11c9b642d930288d14b7ade04673dd98fc8 100644
--- a/chrome/common/extensions/docs/examples/extensions/benchmark/background.html
+++ b/chrome/common/extensions/docs/examples/extensions/benchmark/background.html
@@ -322,6 +322,20 @@ chrome.extension.onConnect.addListener(function(port) {
 });
 
 function run() {
+  if (window.clearCache) {
+    // Show a warning if we will try to clear the cache between runs
+    // but will also be reusing the same WebKit instance (i.e. Chrome
+    // is in single-process mode, or 'Use New Tabs' is turned off)
+    // because the WebKit cache might not get completely cleared between runs.
+    if (chrome.benchmarking.isSingleProcess()) {
+      alert("Warning: the WebKit cache may not be cleared correctly " +
+            "between runs because Chrome is running in single-process mode.");
+    } else if (!window.useNewTabs) {
+      alert("Warning: the WebKit cache may not be cleared correctly " +
+            "between runs because 'Use New Tabs Per Page' is turned off.");
+    }
+  }
+
   var urls = testUrl.split(",");
   for (var i = 0; i < urls.length; i++) {
     var benchmark = new Benchmark();