Add an option to pick a different adb binary.

This will let the recipes use the copy pulled from Chromium's android_tools.

BUG=26

Change-Id: Ica6519223b9fb6daef30f3e14c72ef6422de0f6c
Reviewed-on: https://boringssl-review.googlesource.com/7982
Reviewed-by: Adam Langley <agl@google.com>

util/run_android_tests.go

diff --git a/util/run_android_tests.go b/util/run_android_tests.go
index be9e6c6..9d8f2da 100644
--- a/util/run_android_tests.go
+++ b/util/run_android_tests.go
@@ -28,6 +28,7 @@
 
 var (
 	buildDir     = flag.String("build-dir", "build", "Specifies the build directory to push.")
+	adbPath      = flag.String("adb", "adb", "Specifies the adb binary to use. Defaults to looking in PATH.")
 	device       = flag.String("device", "", "Specifies the device or emulator. See adb's -s argument.")
 	aarch64      = flag.Bool("aarch64", false, "Build the test runners for aarch64 instead of arm.")
 	arm          = flag.Int("arm", 7, "Which arm revision to build for.")
@@ -49,7 +50,7 @@
 	if len(*device) > 0 {
 		args = append([]string{"-s", *device}, args...)
 	}
-	cmd := exec.Command("adb", args...)
+	cmd := exec.Command(*adbPath, args...)
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr
 	return cmd.Run()