Added instructions on how to use code coverage.
Added coverage.md file for emma code coverage instructions for both
instrumentation and junit tests.
BUG=608085
Review-Url: https://codereview.chromium.org/2031743002
Cr-Commit-Position: refs/heads/master@{#397474}
diff --git a/build/android/docs/coverage.md b/build/android/docs/coverage.md
new file mode 100644
index 0000000..0a17987
--- /dev/null
+++ b/build/android/docs/coverage.md
@@ -0,0 +1,32 @@
+# Android code coverage instructions
+
+This is instruction for code coverage for android instrumentation and junit tests.
+
+[TOC]
+
+## How EMMA coverage works
+
+In order to use EMMA code coverage, we need to create build time **.em** file and runtime
+**.ec** file. Then we need to process them using the
+build/android/generate_emma_html.py script.
+
+## How to collect EMMA coverage data
+
+1. Build your APK with the GN arg emma_coverage=true.
+ ```
+ gn args out-gn/Debug
+ > target_os = "android"
+ > emma_coverage = true
+ ```
+ By doing so, **.em** files will be created in out-gn/Debug.
+2. Run tests, with option `--coverage-dir <directory>`, to specify where to save
+ the .ec file. For example, you can run chrome junit tests:
+ `out-gn/Debug/bin/run_chrome_junit_tests --coverage-dir /tmp/coverage`.
+3. Now we have both .em and .ec files. We can merge them and create a html file,
+ using generate_emma_html.py. For example, generate_emma_html.py can be called
+ this way:
+ `build/android/generate_emma_html.py --coverage-dir /tmp/coverage/
+ --metadata-dir out-gn/Debug/ --output example.html`.
+ Then an example.html containing coverage info will be created:
+ `EMMA: writing [html] report to
+ [<your_current_directory>/example.html] …`
