Enable emma code coverage for JUnit testcases.

build/config/android/internal_rules.gni

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/zip.gni")
 import("//third_party/ijar/ijar.gni")
 
 assert(is_android)
@@ skipping 222 matching lines @@
       "--depfile",
       rebase_path(depfile, root_build_dir),
       "--output",
       rebase_path(java_script, root_build_dir),
       "--classpath=@FileArg($_rebased_build_config:java:full_classpath)",
       "--jar-path",
       rebase_path(_jar_path, root_build_dir),
       "--main-class",
       _main_class,
     ]
+    if (emma_coverage) {
+      args += [
+        "--classpath",
+        rebase_path(
+            "//third_party/android_tools_internal/sdk/tools/lib/emma.jar",
+            root_out_dir),

[mikecase (-- gone --), 2016/04/26 17:59:36]

Not 100% sure, but I think you want root_build_dir instead of root_out_dir. Im
not really clear on the difference between them, but there is some info here...
https://chromium.googlesource.com/chromium/src/+/master/tools/gn/docs/referen...

[agrieve, 2016/04/26 18:10:16]

Ah, yeah, that's true. 

The two values are different only when executing in the non-default toolchain
(e.g. host_toolchain). root_build_dir is what scripts always run in.

+      ]
+      args += [ "--noverify" ]
+    }
     if (defined(invoker.wrapper_script_args)) {
       args += [ "--" ] + invoker.wrapper_script_args
     }
     if (defined(invoker.bootclasspath)) {
       inputs += [ invoker.bootclasspath ]
       args += [
         "--bootclasspath",
         rebase_path(invoker.bootclasspath, root_build_dir),
       ]
     }
@@ skipping 1967 matching lines @@
 
     args = [
       "--depfile",
       rebase_path(depfile, root_build_dir),
       "--script-output-path",
       rebase_path(generated_script, root_build_dir),
     ]
     args += test_runner_args
   }
 }