Add cpu_stats for the browser

tools/telemetry/telemetry/core/browser_unittest.py

Index: tools/telemetry/telemetry/core/browser_unittest.py
diff --git a/tools/telemetry/telemetry/core/browser_unittest.py b/tools/telemetry/telemetry/core/browser_unittest.py
index bf7332560046239f3df0c87bb9f14679c6cb17de..60699318e91c6777aad1939011e28cac5644ee1f 100644
--- a/tools/telemetry/telemetry/core/browser_unittest.py
+++ b/tools/telemetry/telemetry/core/browser_unittest.py
@@ -49,6 +49,8 @@ class BrowserTest(unittest.TestCase):
   def tearDown(self):
     if self._browser:
       self._browser.Close()
+    self._browser = None
+
 
   def testBrowserCreation(self):
     b = self.CreateBrowser()
@@ -143,3 +145,18 @@ class BrowserTest(unittest.TestCase):
     for g in info.gpu.devices:
       self.assertTrue(isinstance(g, gpu_device.GPUDevice))
 
+  def testRendererCpuInfo(self):
+    b = self.CreateBrowser()
+    b.tabs[0].Navigate(b.http_server.UrlOf('blank.html'))
+    b.tabs[0].WaitForDocumentReadyStateToBeInteractiveOrBetter()
+    low_cpu_load = b.cpu_stats
+    self.tearDown()
+
+    b = self.CreateBrowser()
+    b.tabs[0].Navigate(b.http_server.UrlOf('high_cpu.html'))
+    b.tabs[0].WaitForDocumentReadyStateToBeInteractiveOrBetter()
+    high_cpu_load = b.cpu_stats
+    self.tearDown()
+
+    self.assertTrue(high_cpu_load['Renderer'].get('CpuPercent', 0) >=
+                    low_cpu_load['Renderer'].get('CpuPercent', 0))