Android: Fix isTablet()-related occuring on some JB tablets

A better fix would be fix PhysicalDisplayAndroid.java, but given this is
fixed in JB MR1, I don't think it's worth the extra effort.

Bug: 829318
Change-Id: Ibe03c8392bf86b69322ff01f9ddf3c63396a161f
Reviewed-on: https://chromium-review.googlesource.com/1001707
Commit-Queue: agrieve <agrieve@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549274}

ui/android/java/src/org/chromium/ui/base/DeviceFormFactor.java

@@ -5,6 +5,7 @@
 package org.chromium.ui.base;
 
 import android.content.Context;
+import android.os.Build;
 import android.support.annotation.UiThread;
 
 import org.chromium.base.ContextUtils;
@@ -86,9 +87,12 @@ public class DeviceFormFactor {
     }
 
     private static int detectScreenWidthBucket(Context context) {
-        // TODO(agrieve): Remove runningOnUiThread() guard and audit for background thread usages.
-        //     https://crbug.com/669974
-        if (ThreadUtils.runningOnUiThread()
+        // Pre-JB MR1, Display.getSize() is used rather than Display.getRealSize().
+        // For our query, getSize() is not always correct. https://crbug.com/829318
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1
+                // TODO(agrieve): Remove thread check and audit for background usages.
+                //     https://crbug.com/669974
+                && ThreadUtils.runningOnUiThread()
                 && !isTabletDisplay(DisplayAndroid.getNonMultiDisplay(context))) {
             // There have been no cases where tablet resources end up being used on phone-sized
             // displays. Short-circuit this common-case since checking resources is slower (and

ui/android/java/src/org/chromium/ui/display/DisplayAndroid.java

@@ -85,6 +85,8 @@ public class DisplayAndroid {
     }
 
     /**
+     * Note: For JB pre-MR1, this can sometimes return values smaller than the actual screen.
+     * https://crbug.com/829318
      * @return Display height in physical pixels.
      */
     public int getDisplayHeight() {
@@ -92,6 +94,7 @@ public class DisplayAndroid {
     }
 
     /**
+     * Note: For JB pre-MR1, this can sometimes return values smaller than the actual screen.
      * @return Display width in physical pixels.
      */
     public int getDisplayWidth() {