Exit fullscreen when Reader Mode infobar is tapped

Since it is possible for the Reader Mode infobar to appear while a
tab is in fullscreen mode, activating the feature should exit
fullscreen. This change toggles fullscreen mode just before navigating
to reader content.

BUG=735383

Change-Id: Ic6133a3423767583df0efcc2df3e6ae3d0c915ef
Reviewed-on: https://chromium-review.googlesource.com/544076Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#481684}

chrome/android/java/src/org/chromium/chrome/browser/dom_distiller/ReaderModeManager.java

@@ -396,6 +396,8 @@ public class ReaderModeManager extends TabModelSelectorTabObserver {
         ReaderModeTabInfo info = mTabStatusMap.get(mTabModelSelector.getCurrentTabId());
         if (info != null) info.onStartedReaderMode();
 
+        // Make sure to exit fullscreen mode before navigating.
+        mTabModelSelector.getCurrentTab().toggleFullscreenMode(false);
         DomDistillerTabUtils.distillCurrentPageAndView(getBasePageWebContents());
     }