[EoC + Duet] Center the EoC icon in its bounding box

Center the EoC icon in its bounding box when Duet is enabled.

BUG=859592

Change-Id: I7c1e016e2454ab5abb212c229b3b16450b553e7b
Reviewed-on: https://chromium-review.googlesource.com/1166245Reviewed-by: Matthew Jones <mdjones@chromium.org>
Commit-Queue: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581699}

chrome/android/java/src/org/chromium/chrome/browser/toolbar/ToolbarPhone.java

@@ -2815,6 +2815,10 @@ public class ToolbarPhone extends ToolbarLayout
         if (mExperimentalButton == null) {
             ViewStub viewStub = findViewById(R.id.experimental_button_stub);
             mExperimentalButton = (TintedImageButton) viewStub.inflate();
+
+            if (FeatureUtilities.isBottomToolbarEnabled()) {
+                mExperimentalButton.setPadding(0, 0, 0, 0);
+            }
         } else {
             assert mExperimentalButton.getVisibility()
                     == View.GONE : "#disableExperimentalButton() should be called first.";