Fix typo in histogram name.

The CL https://codereview.chromium.org/943823002/ introduced a new
histogram for whether web pages are assumed to be mobile friendly.

However, there was a typo in recording the histogram name.

This fixes the recording part to match the histogram.

BUG=462721

Review URL: https://codereview.chromium.org/965883002

Cr-Commit-Position: refs/heads/master@{#318532}

chrome/android/java/src/org/chromium/chrome/browser/Tab.java

@@ -1360,7 +1360,7 @@ public class Tab implements ViewGroup.OnHierarchyChangeListener,
         updateFullscreenEnabledState();
         if (!isNativePage()) {
             RecordHistogram.recordBooleanHistogram(
-                    "Navigation.MobileOptimized", mContentViewCore.getIsMobileOptimizedHint());
+                    "Navigation.IsMobileOptimized", mContentViewCore.getIsMobileOptimizedHint());
         }
 
         for (TabObserver observer : mObservers) observer.onPageLoadFinished(this);