Pass webview instance when getting base layer / color, and prevent null value

Depends on external/webkit change: https://android-git.corp.google.com/g/#/c/188470/

bug:6429897
Change-Id: Ic948f102034dbe57c61d7fc6de73a4ddd062f686

Author: ChrisCraik

core/java/android/webkit/WebViewClassic.java

@@ -3299,7 +3299,8 @@ public int getContentWidth() {
     }
 
     public int getPageBackgroundColor() {
-        return nativeGetBackgroundColor();
+        if (mNativeClass == 0) return Color.WHITE;
+        return nativeGetBackgroundColor(mNativeClass);
     }
 
     /**
@@ -4456,7 +4457,7 @@ int getBaseLayer() {
         if (mNativeClass == 0) {
             return 0;
         }
-        return nativeGetBaseLayer();
+        return nativeGetBaseLayer(mNativeClass);
     }
 
     private void onZoomAnimationStart() {
@@ -8593,7 +8594,7 @@ private native void     nativeUpdateDrawGLFunction(int nativeInstance, Rect invS
     private native void     nativeSetHeightCanMeasure(boolean measure);
     private native boolean  nativeSetBaseLayer(int nativeInstance,
             int layer, boolean showVisualIndicator, boolean isPictureAfterFirstLayout);
-    private native int      nativeGetBaseLayer();
+    private native int      nativeGetBaseLayer(int nativeInstance);
     private native void     nativeCopyBaseContentToPicture(Picture pict);
     private native boolean  nativeHasContent();
     private native void     nativeStopGL();
@@ -8621,7 +8622,7 @@ private native int      nativeScrollableLayer(int nativeInstance, int x, int y,
      */
     private native boolean  nativeScrollLayer(int nativeInstance, int layer, int newX, int newY);
     private native void     nativeSetIsScrolling(boolean isScrolling);
-    private native int      nativeGetBackgroundColor();
+    private native int      nativeGetBackgroundColor(int nativeInstance);
     native boolean  nativeSetProperty(String key, String value);
     native String   nativeGetProperty(String key);
     /**