Make telemetry platform a singleton

tools/telemetry/telemetry/core/platform/android_platform_backend.py

Index: tools/telemetry/telemetry/core/platform/android_platform_backend.py
diff --git a/tools/telemetry/telemetry/core/platform/android_platform_backend.py b/tools/telemetry/telemetry/core/platform/android_platform_backend.py
index 3da4c25d2ea65775e02d8c9024f4c732aee9b209..471014c931b5ff084fe06aeacc1e6ce58268a679 100644
--- a/tools/telemetry/telemetry/core/platform/android_platform_backend.py
+++ b/tools/telemetry/telemetry/core/platform/android_platform_backend.py
@@ -7,9 +7,9 @@ import tempfile
 
 from telemetry import decorators
 from telemetry.core import exceptions
-from telemetry.core import platform
 from telemetry.core import util
 from telemetry.core import video
+from telemetry.core import platform as platform_module
 from telemetry.core.platform import proc_supporting_platform_backend
 from telemetry.core.platform.power_monitor import android_ds2784_power_monitor
 from telemetry.core.platform.power_monitor import android_dumpsys_power_monitor
@@ -79,7 +79,7 @@ class AndroidPlatformBackend(
     self._surface_stats_collector.Stop()
     for r in self._surface_stats_collector.GetResults():
       self._raw_display_frame_rate_measurements.append(
-          platform.Platform.RawDisplayFrameRateMeasurement(
+          platform_module.Platform.RawDisplayFrameRateMeasurement(
               r.name, r.value, r.unit))
 
     self._surface_stats_collector = None
@@ -188,7 +188,7 @@ class AndroidPlatformBackend(
   def LaunchApplication(
       self, application, parameters=None, elevate_privilege=False):
     if application in _HOST_APPLICATIONS:
-      platform.GetHostPlatform().LaunchApplication(
+      platform_module.GetHostPlatform().LaunchApplication(
           application, parameters, elevate_privilege=elevate_privilege)
       return
     if elevate_privilege:
@@ -199,17 +199,17 @@ class AndroidPlatformBackend(
 
   def IsApplicationRunning(self, application):
     if application in _HOST_APPLICATIONS:
-      return platform.GetHostPlatform().IsApplicationRunning(application)
+      return platform_module.GetHostPlatform().IsApplicationRunning(application)
     return len(self._device.GetPids(application)) > 0
 
   def CanLaunchApplication(self, application):
     if application in _HOST_APPLICATIONS:
-      return platform.GetHostPlatform().CanLaunchApplication(application)
+      return platform_module.GetHostPlatform().CanLaunchApplication(application)
     return True
 
   def InstallApplication(self, application):
     if application in _HOST_APPLICATIONS:
-      platform.GetHostPlatform().InstallApplication(application)
+      platform_module.GetHostPlatform().InstallApplication(application)
       return
     raise NotImplementedError(
         'Please teach Telemetry how to install ' + application)