customtabs: Make sure that the browser process is initialized in mayLaunchUrl().

Since the documentation doesn't force clients to call warmup() before
mayLaunchUrl(), call warmup() for them inside mayLaunchUrl() if
necessary.

BUG=525002

Review URL: https://codereview.chromium.org/1311423003

Cr-Commit-Position: refs/heads/master@{#345590}
(cherry picked from commit d9879f1dc467a031829d5a769f572b99b5c37463)

TBR=yusufo@chromium.org
NOTRY=true
NOPRESUBMIT=true

Review URL: https://codereview.chromium.org/1316973004 .

Cr-Commit-Position: refs/branch-heads/2454@{#430}
Cr-Branched-From: 12bfc3360892ec53cd00fc239a47e5298beb063b-refs/heads/master@{#338390}

• chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabsConnection.java[diff]