customtabs: Make sure that the browser process is initialized in mayL…

…aunchUrl().

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 d9879f1)

Review URL: https://codereview.chromium.org/1315893003 .

Cr-Commit-Position: refs/branch-heads/2490@{#42}
Cr-Branched-From: 7790a35-refs/heads/master@{#344925}

chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabsConnection.java

@@ -319,6 +319,9 @@ public boolean mayLaunchUrl(ICustomTabsCallback callback, Uri url, final Bundle
         if (scheme != null && !scheme.equals("http") && !scheme.equals("https")) return false;
         if (!isCallerForegroundOrSelf()) return false;
 
+        // Things below need the browser process to be initialized.
+        if (!warmup(0)) return false;
+
         final IBinder session = callback.asBinder();
         final String urlString = url.toString();
         final boolean noPrerendering =