Show soft keyboard when omnibox focused

Explicitly show soft input keypboard on omnibox focus for search. Fixes
an issue with Duet, where the keyboard could be dismissed by the Back
or keyboard Action buttons, after which re-clicking the Search button
would focus the omnibox, but would not re-open the keyboard by default.

Bug: 981682
Change-Id: I1fe14edae4493dd57afe79250ad7fdbc806adcc5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1869530Reviewed-by: Ender <ender@google.com>
Reviewed-by: Theresa  <twellington@chromium.org>
Reviewed-by: Matthew Jones <mdjones@chromium.org>
Commit-Queue: Natalie Chouinard <chouinard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710973}

chrome/android/java/src/org/chromium/chrome/browser/omnibox/LocationBarLayout.java

@@ -994,6 +994,11 @@ public class LocationBarLayout extends FrameLayout
                 handleUrlFocusAnimation(mUrlHasFocus);
             } else {
                 mUrlBar.requestFocus();
+
+                // Explicitly show soft keyboard (crbug.com/981682).
+                InputMethodManager imm = (InputMethodManager) getContext().getSystemService(
+                        Context.INPUT_METHOD_SERVICE);
+                imm.showSoftInput(mUrlBar, 0);
             }
         } else {
             assert pastedText == null;