Android: Don't keep all Services in main dex.

Reduces main dex by 4500 methods

TBR=agrieve  # Trivial change to DecoderService

Bug: 820570
Change-Id: Ifeeb0cc768dd762c58c6a11061a17e73e12e38a1
Reviewed-on: https://chromium-review.googlesource.com/966877Reviewed-by: agrieve <agrieve@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: agrieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544059}

build/android/main_dex_classes.flags

@@ -22,8 +22,16 @@
   *;
 }
 
--keep public class * extends android.app.Service {
-  <init>();
+-keep public class * extends org.chromium.base.process_launcher.ChildProcessService {
+  *;
+}
+
+-keep public class com.android.webview.** {
+  *;
+}
+
+-keep public class org.chromium.android_webview.** {
+  *;
 }
 
 # Used by tests for secondary dex extraction.

chrome/android/java/src/org/chromium/chrome/browser/photo_picker/DecoderService.java

@@ -16,6 +16,7 @@ import android.os.SystemClock;
 import org.chromium.base.Log;
 import org.chromium.base.PathUtils;
 import org.chromium.base.ThreadUtils;
+import org.chromium.base.annotations.MainDex;
 import org.chromium.base.library_loader.LibraryLoader;
 import org.chromium.base.library_loader.LibraryProcessType;
 import org.chromium.base.library_loader.ProcessInitException;
@@ -27,6 +28,7 @@ import java.io.IOException;
 /**
  * A service to accept requests to take image file contents and decode them.
  */
+@MainDex
 public class DecoderService extends Service {
     // The keys for the bundle when passing data to and from this service.
     static final String KEY_FILE_DESCRIPTOR = "file_descriptor";