Revert "Remove //chrome/android:chrome alias"

This reverts commit e3f445df.

Reason for revert: 
Broke compile: https://build.chromium.org/p/chromium.android/builders/Android%20Cronet%20KitKat%20Builder/builds/3365

Original change's description:
> Remove //chrome/android:chrome alias
> 
> Downstream rename is now complete.
> 
> Bug: 731186
> Change-Id: I78be4e134d0a4ea0cf98c714f92d4835902de5e9
> Reviewed-on: https://chromium-review.googlesource.com/684956
> Reviewed-by: Tommy Nyquist <nyquist@chromium.org>
> Commit-Queue: Andrew Grieve <agrieve@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#504437}

TBR=nyquist@chromium.org,agrieve@chromium.org

Change-Id: I65a66e72aabc72986c8e9aacef485807cab98c3c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 731186
Reviewed-on: https://chromium-review.googlesource.com/685635Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#504444}

chrome/android/BUILD.gn

@@ -702,6 +702,13 @@ jinja_template_resources("chrome_sync_shell_apk_template_resources") {
   variables = chrome_sync_shell_jinja_variables
 }
 
+# TODO(agrieve): Delete target once downstream references are removed.
+group("chrome") {
+  public_deps = [
+    ":libchrome",
+  ]
+}
+
 shared_library("libchrome") {
   sources = [
     "../app/android/chrome_main_delegate_android_initializer.cc",