[telemetry] Detect and correct overflow in Intel energy MSRs.

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 2b9ce567cff586adb84ab33b0579b916d231f1d8..a6fb125d0adf3637b7f12eddda5fe86fa23d50e0 100644
--- a/tools/telemetry/telemetry/core/platform/platform_backend.py
+++ b/tools/telemetry/telemetry/core/platform/platform_backend.py
@@ -226,10 +226,16 @@ class PlatformBackend(object):
   def StopMonitoringPower(self):
     raise NotImplementedError()
 
-  def ReadMsr(self, msr_number):
+  def ReadMsr(self, msr_number, start=0, length=64):
     """Read a CPU model-specific register (MSR).
 
     Which MSRs are available depends on the CPU model.
     On systems with multiple CPUs, this function may run on any CPU.
+
+    Args:
+      msr_number: The number of the register to read.
+      start: The least significant bit to read, zero-indexed.
+          (Said another way, the number of bits to right-shift the MSR value.)
+      length: The number of bits to read. MSRs are 64 bits, even on 32-bit CPUs.
     """
     raise NotImplementedError()