More complete implementation for condition and log matchers in statsd.

+ also synced proto from google3 to fix the LogEntryMatcher proto

+ MetricsManager represents StatsdConfig, it's responsible for initializing and managing all
LogEntryMatcher, Condition, and Metrics. Start review from here.

+ Added more complete StatsdConfig initialization, including building the map for:
    LogEntryMatcher -> Metrics
    LogEntryMatcher -> Condition
    Condition       -> Metrics.

    All the maps use index(int). The extra amount of memory for storing mappings help us
    quickly process log events.

  The StatsdConfig initialization process detects malformed config
  - Circle dependency
  - Missing definition
  etc.

 And once we detect ANY error, statsd will reject the config. And the resources related to this
 config will be released.

Test: Added unit tests
Change-Id: I2c4aefdbf3e2aa1701eacbb2fb5e653819ec1fbb