Check if tab is null before requesting theme color

chrome/android/java/src/org/chromium/chrome/browser/compositor/scene_layer/ToolbarSceneLayer.java

Index: chrome/android/java/src/org/chromium/chrome/browser/compositor/scene_layer/ToolbarSceneLayer.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/compositor/scene_layer/ToolbarSceneLayer.java b/chrome/android/java/src/org/chromium/chrome/browser/compositor/scene_layer/ToolbarSceneLayer.java
index 8335b4b870589348dc899e326ac40e0787f54d21..757c727a453027ef99f7ad88bf56d89fc2974efa 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/compositor/scene_layer/ToolbarSceneLayer.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/compositor/scene_layer/ToolbarSceneLayer.java
@@ -149,9 +149,10 @@ public class ToolbarSceneLayer extends SceneOverlayLayer implements SceneOverlay
         // TODO(mdjones): Create a "theme provider" to handle cases like this.
         int color = mRenderHost.getBrowserControlsBackgroundColor();
         float alpha = mRenderHost.getBrowserControlsUrlBarAlpha();
-        if (mLayoutProvider.getFullscreenManager().areBrowserControlsAtBottom()) {
-            color = mLayoutProvider.getFullscreenManager().getTab().getDefaultThemeColor();
-            if (!mLayoutProvider.getFullscreenManager().getTab().isIncognito()) alpha = 1f;
+        ChromeFullscreenManager fullscreenManager = mLayoutProvider.getFullscreenManager();
+        if (fullscreenManager.areBrowserControlsAtBottom() && fullscreenManager.getTab() != null) {
+            color = fullscreenManager.getTab().getDefaultThemeColor();
+            if (!fullscreenManager.getTab().isIncognito()) alpha = 1f;
         }
 
         update(color, alpha, mLayoutProvider.getFullscreenManager(), resourceManager,