Centralize mojo_benchmark documentation.

This patch removes the duplication between mojo_benchmark built-in help
and mojo_benchmark.md documentation. The built-in help now points to the
Markdown documentation.

R=qsr@chromium.org

Review URL: https://codereview.chromium.org/1423233002 .

Cr-Mirrored-From: https://github.com/domokit/mojo
Cr-Mirrored-Commit: 158137d99a91b98774f3b13787b8b9d6fcde4958

docs/mojo_benchmark.md

diff --git a/docs/mojo_benchmark.md b/docs/mojo_benchmark.md
index bcca1ad..f9cb773 100644
--- a/docs/mojo_benchmark.md
+++ b/docs/mojo_benchmark.md
@@ -12,7 +12,7 @@
 ## Defining benchmarks
 
 `mojo_benchmark` runs performance tests defined in a benchmark file. The
-benchmark file is a Python dictionary of the following format:
+benchmark file is a Python program setting a dictionary of the following format:
 
 ```python
 benchmarks = [
@@ -24,35 +24,72 @@
 
     # List of measurements to make.
     'measurements': [
-      '<measurement type>/<event category>/<event name>',
+      {
+        'name': <my_measurement>,
+        'spec': <spec>,
+      },
+      (...)
     ],
   },
 ]
 ```
 
+The benchmark file may reference the `target_os` global that will be any of
+('android', 'linux'), indicating the system on which the benchmarks are run.
+
+### Measurement specs
+
 The following types of measurements are available:
 
- - `time_until` - measures time until the first occurence of the specified event
- - `avg_duration` - measures the average duration of all instances of the 
-    specified event
+  - `time_until`
+  - `time_between`
+  - `avg_duration`
+  - `percentile_duration`
+
+`time_until` records the time until the first occurence of the targeted event.
+The underlying benchmark runner records the time origin just before issuing the
+connection call to the application being benchmarked. Results of `time_until`
+measurements are relative to this time. Spec format:
+
+```
+'time_until/<category>/<event>'
+```
+
+`time_between` records the time between the first occurence of the first
+targeted event and the first occurence of the second targeted event. Spec
+format:
+
+```
+'time_between/<category1>/<event1>/<category2>/<event2>'
+```
+
+`avg_duration` records the average duration of all occurences of the targeted
+event. Spec format:
+
+```
+'avg_duration/<category>/<event>'
+```
+
+`percentile_duration` records the value at the given percentile of durations of
+all occurences of the targeted event. Spec format:
+
+```
+'percentile_duration/<category>/<event>/<percentile>'
+```
+
+where `<percentile>` is a number between 0.0 and 0.1.
 
 ## Caching
 
 The script runs each benchmark twice. The first run (**cold start**) clears
 caches of the following apps on startup:
 
- - network_service.mojo
- - url_response_disk_cache.mojo
+ - `network_service.mojo`
+ - `url_response_disk_cache.mojo`
 
 The second run (**warm start**) runs immediately afterwards, without clearing
 any caches.
 
-## Time origin
-
-The underlying benchmark runner records the time origin just before issuing the
-connection call to the application being benchmarked. Results of `time_until`
-measurements are relative to this time.
-
 ## Example
 
 For an app that records a trace event named "initialized" in category "my_app"

mojo_benchmark

diff --git a/mojo_benchmark b/mojo_benchmark
index 4a5c6fe..fc0258e 100755
--- a/mojo_benchmark
+++ b/mojo_benchmark
@@ -20,47 +20,8 @@
 _DESCRIPTION = """Runner for Mojo application benchmarks.
 
 |benchmark_list_file| has to be a valid Python program that sets a |benchmarks|
-global variable, containing entries of the following form:
-
-  {
-    'name': '<name of the benchmark>',
-    'app': '<url of the app to benchmark>',
-    'shell-args': [],
-    'duration': <duration in seconds>,
-
-    # List of measurements to make.
-    'measurements': [
-      {
-        'name': my_measurement,
-        'spec': spec,
-      },
-      (...)
-    ]
-  }
-
-For each measurement, 'name' is a label used for presentation purposes. 'spec'
-defines the measurement.
-
-Available measurement types are:
-
-'time_until' - time until the first occurence of the targeted event. The spec
-takes the following format:
-
-  'time_until/category/event'
-
-'avg_duration' - average duration of the targeted event. The spec takes the
-following format:
-
-  'avg_duration/category/event'
-
-'percentile_duration' - value at the given percentile of the targeted event. The
-spec takes the following format:
-
-  'percentile_duration/category/event/percentile'
-
-|benchmark_list_file| may reference the |target_os| global that will be any of
-['android', 'linux'], indicating the system on which the benchmarks are to be
-run.
+dictionary. For description of the required format see
+https://github.com/domokit/devtools/blob/master/docs/mojo_benchmark.md .
 """
 
 _logger = logging.getLogger()