Using decorator for power monitoring.

tools/telemetry/telemetry/page/page_measurement.py

Index: tools/telemetry/telemetry/page/page_measurement.py
diff --git a/tools/telemetry/telemetry/page/page_measurement.py b/tools/telemetry/telemetry/page/page_measurement.py
index dcaa8b0dd6ef08ddce635f772764f93f9d4fe5d6..ad180c9332ce95dce898f19e631017296db66063 100644
--- a/tools/telemetry/telemetry/page/page_measurement.py
+++ b/tools/telemetry/telemetry/page/page_measurement.py
@@ -51,6 +51,7 @@ class PageMeasurement(page_test.PageTest):
 
   def _RunTest(self, page, tab, results):
     results.WillMeasurePage(page)
+    self.WillMeasurePage(page, tab)
     try:
       self.MeasurePage(page, tab, results)
     finally:
@@ -66,6 +67,15 @@ class PageMeasurement(page_test.PageTest):
     run."""
     return True
 
+  def WillMeasurePage(self, page, tab):
+    """Override to execute any actions needed prior to measurement.
+
+    A usual behavior is to wait for the intersting action on the page to be
+    finished.
+
+    By default, does nothing."""
+    pass
+
   def MeasurePage(self, page, tab, results):
     """Override to actually measure the page's performance.