[Home] Do not intercept back button if in fullscreen mode

While in fullscreen mode, the bottom sheet should not intercept the
back button; exiting fullscreen should take priority. This change
moves the fullscreen check in ChromeTabbedActivity so that it is handled
before the bottom sheet has a chance to intercept it.

BUG=762481

Change-Id: I1def229ae8329b3028a7e9fe37b803ef3d1a3bf4
Reviewed-on: https://chromium-review.googlesource.com/653178
Reviewed-by: Theresa <twellington@chromium.org>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#500111}

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

@@ -1702,6 +1702,11 @@ public boolean handleBackPressed() {
         if (!mUIInitialized) return false;
         final Tab currentTab = getActivityTab();
 
+        if (exitFullscreenIfShowing()) {
+            recordBackPressedUma("Exited fullscreen", BACK_PRESSED_EXITED_FULLSCREEN);
+            return true;
+        }
+
         if (getBottomSheet() != null && getBottomSheet().handleBackPress()) return true;
 
         if (currentTab == null) {
@@ -1717,11 +1722,6 @@ public boolean handleBackPressed() {
             return true;
         }
 
-        if (exitFullscreenIfShowing()) {
-            recordBackPressedUma("Exited fullscreen", BACK_PRESSED_EXITED_FULLSCREEN);
-            return true;
-        }
-
         if (getToolbarManager().back()) {
             recordBackPressedUma("Navigating backward", BACK_PRESSED_NAVIGATED_BACK);
             return true;