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

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

Index: android_webview/java/src/org/chromium/android_webview/AwContents.java
diff --git a/android_webview/java/src/org/chromium/android_webview/AwContents.java b/android_webview/java/src/org/chromium/android_webview/AwContents.java
index 23e1a053b0e2f451919e019ce28983f8f8b2b40f..c8796acaf8241abfeae43317af42c4830bf8c2ab 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwContents.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwContents.java
@@ -1977,6 +1977,9 @@ public class AwContents {
         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));