[Telemetry] Allow memory info to go missing on non-rooted devices.

tools/telemetry/telemetry/core/browser.py

Index: tools/telemetry/telemetry/core/browser.py
diff --git a/tools/telemetry/telemetry/core/browser.py b/tools/telemetry/telemetry/core/browser.py
index c317e6a248068e21278e08fa0d926c4ae8925050..6a3c6ca0fa1f177e0ba5b8520523884139d89aa7 100644
--- a/tools/telemetry/telemetry/core/browser.py
+++ b/tools/telemetry/telemetry/core/browser.py
@@ -177,10 +177,12 @@ class Browser(object):
     """
     self._platform_backend.PurgeUnpinnedMemory()
     result = self._GetStatsCommon(self._platform_backend.GetMemoryStats)
-    result['SystemCommitCharge'] = \
-        self._platform_backend.GetSystemCommitCharge()
-    result['SystemTotalPhysicalMemory'] = \
-        self._platform_backend.GetSystemTotalPhysicalMemory()
+    commit_charge = self._platform_backend.GetSystemCommitCharge()
+    if commit_charge:
+      result['SystemCommitCharge'] = commit_charge
+    total = self._platform_backend.GetSystemTotalPhysicalMemory()
+    if total:
+      result['SystemTotalPhysicalMemory'] = total
     return result
 
   @property