Move remote platforms creation logic from android_browser_finder to platform

tools/telemetry/telemetry/core/platform/platform_backend.py

Index: tools/telemetry/telemetry/core/platform/platform_backend.py
diff --git a/tools/telemetry/telemetry/core/platform/platform_backend.py b/tools/telemetry/telemetry/core/platform/platform_backend.py
index 710b8e596d45cffa86725b5d2f5496ca53cf3600..2b9ce567cff586adb84ab33b0579b916d231f1d8 100644
--- a/tools/telemetry/telemetry/core/platform/platform_backend.py
+++ b/tools/telemetry/telemetry/core/platform/platform_backend.py
@@ -44,7 +44,19 @@ YOSEMITE =     OSVersion('yosemite',     1010)
 
 
 class PlatformBackend(object):
-  def __init__(self):
+
+  def __init__(self, device=None):
+    """ Initalize an instance of PlatformBackend from a device optionally.
+      Call sites need to use SupportsDevice before intialization to check
+      whether this platform backend supports the device.
+      If device is None, this constructor returns the host platform backend
+      which telemetry is running on.
+
+      Args:
+        device: an instance of telemetry.core.platform.device.Device.
+    """
+    if device and not self.SupportsDevice(device):
+      raise ValueError('Unsupported device: %s' % device.name)
     self._platform = None
     self._running_browser_backends = weakref.WeakSet()
     self._tracing_controller_backend = (
@@ -52,6 +64,12 @@ class PlatformBackend(object):
     self._profiling_controller_backend = (
         profiling_controller_backend.ProfilingControllerBackend(self))
 
+  @classmethod
+  def SupportsDevice(cls, device):
+    """ Returns whether this platform backend supports intialization from the
+    device. """
+    return False
+
   def SetPlatform(self, platform):
     assert self._platform == None
     self._platform = platform