[android_webview] Update max scroll offset from page scale change.

android_webview/java/src/org/chromium/android_webview/AwContents.java

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.android_webview;
 
 import android.annotation.SuppressLint;
 import android.app.Activity;
 import android.content.ComponentCallbacks2;
 import android.content.Context;
@@ skipping 1959 matching lines @@
         if (mPageScaleFactor == pageScaleFactor &&
                 mMinPageScaleFactor == minPageScaleFactor &&
                 mMaxPageScaleFactor == maxPageScaleFactor) {
             return;
         }
         mMinPageScaleFactor = minPageScaleFactor;
         mMaxPageScaleFactor = maxPageScaleFactor;
         if (mPageScaleFactor != pageScaleFactor) {
           float oldPageScaleFactor = mPageScaleFactor;
           mPageScaleFactor = pageScaleFactor;
+          // NOTE: if this ever needs to become synchronous then we need to make sure the scroll
+          // bounds are correctly updated before calling the method, otherwise embedder code that
+          // attempts to scroll on scale change might cause weird results.
           mContentsClient.getCallbackHelper().postOnScaleChangedScaled(
                   (float)(oldPageScaleFactor * mDIPScale),
                   (float)(mPageScaleFactor * mDIPScale));
         }
     }
 
     @CalledByNative
     private void setAwAutofillManagerDelegate(AwAutofillManagerDelegate delegate) {
         mAwAutofillManagerDelegate = delegate;
         delegate.init(mContentViewCore);
@@ skipping 141 matching lines @@
             long nativeAwContents, boolean value, String requestingFrame);
 
     private native void nativeSetJsOnlineProperty(long nativeAwContents, boolean networkUp);
 
     private native void nativeTrimMemoryOnRenderThread(long nativeAwContents, int level,
             boolean visible);
 
     private native void nativeCreatePdfExporter(long nativeAwContents, AwPdfExporter awPdfExporter);
 
 }