message: Update ProfilerContext documentation to refer to profiler.profile_context instead of tf.contrib.
diff: @@ -115,7 +115,7 @@ class ProfileContext(object):
  ```python
  # Trace steps 100~200, profile at [150, 200] and dump profile at 200.
  - with tf.contrib.tfprof.ProfileContext('/tmp/train_dir',
  + with profile_context.ProfileContext('/tmp/train_dir',
  trace_steps=range(100, 200, 3),
  dump_steps=[200]) as pctx:
  opts = tf.profiler.ProfileOptionBuilder.time_and_memory()
  @@ -123,13 +123,13 @@ class ProfileContext(object):
  train_loop().
  # Tracing only.
  - with tf.contrib.tfprof.ProfileContext('/tmp/train_dir') as pctx:
  + with profile_context.tfprof.ProfileContext('/tmp/train_dir') as pctx:
  # Run train/eval loop for at least few hundred steps. Profiles will be
  # dumped to train_dir. Use web UI or command line to do profiling.
  train_loop().
  # When session object is available, do explicit trace, profile and dump.
  - with tf.contrib.tfprof.ProfileContext('/tmp/train_dir',
  + with profile_context.ProfileContext('/tmp/train_dir',
  trace_steps=[],
  dump_steps=[]) as pctx:
  opts = tf.profiler.ProfileOptionBuilder.time_and_memory()
  