Make channel available in Java via ChromeVersionConstants.java.

chrome/android/BUILD.gn

Index: chrome/android/BUILD.gn
diff --git a/chrome/android/BUILD.gn b/chrome/android/BUILD.gn
index e852cfeadaf438b0e30521f0d2e3850c5dfc8f63..521b767556b9a47a8e7bc6d7611abd92b1a6f433 100644
--- a/chrome/android/BUILD.gn
+++ b/chrome/android/BUILD.gn
@@ -6,6 +6,7 @@ import("//build/config/android/config.gni")
 import("//build/config/android/rules.gni")
 import("//chrome/version.gni")
 import("//third_party/icu/config.gni")
+import("channel.gni")
 
 # GYP: //chrome/chrome.gyp:chrome_java (resources part)
 android_resources("chrome_java_resources") {
@@ -469,6 +470,7 @@ chrome_version_java_file = "$chrome_version_java_dir/org/chromium/chrome/browser
 process_version("chrome_version_java") {
   source = "java/ChromeVersionConstants.java.version"
   output = chrome_version_java_file
+  extra_args = ["-e", "CHANNEL=str.upper('$android_channel')"]
 }
 
 zip("chrome_version_srcjar") {