BrowserWindowCocoa::Show should activate the window
BrowserWindowCocoa::Show should activate the window

When a new tab/window is opened on Mac, the window is currently brought
to the front relative to other Chrome windows, but not relative to other
apps. This often goes unnoticed, since Chrome is often already the
active app, but it's particularly noticeable when clicking on a push
notification opens a new tab/window, as this window will remain
underneath other apps if Chrome wasn't already in the foreground.

This patch makes Show always Activate the window as well.

BUG=470830
TEST=manual, follow steps in https://crbug.com/470830
TBR=avi@chromium.org

Review URL: https://codereview.chromium.org/1166643003

Cr-Commit-Position: refs/heads/master@{#332615}
(cherry picked from commit b13b6d7b2c7ad67c1b1937897fe3c26527eeb943)

Review URL: https://codereview.chromium.org/1165973002

Cr-Commit-Position: d34a0005849006230ae7ffb1a9693419810a06bc@{#198}
Cr-Branched-From: 40cda19e609fd36fbf5fe489055423e611631abc@{#330231}

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