[android_webview] Use auto-sizing for webviews in wrap content mode.

android_webview/java/src/org/chromium/android_webview/AwLayoutSizer.java

Index: android_webview/java/src/org/chromium/android_webview/AwLayoutSizer.java
diff --git a/android_webview/java/src/org/chromium/android_webview/AwLayoutSizer.java b/android_webview/java/src/org/chromium/android_webview/AwLayoutSizer.java
index e09259b0dde7c512091a63f5aeb50f51b2d2a8da..078afcabacd5aa271a7ba06e2d60403ba64bbe75 100644
--- a/android_webview/java/src/org/chromium/android_webview/AwLayoutSizer.java
+++ b/android_webview/java/src/org/chromium/android_webview/AwLayoutSizer.java
@@ -26,6 +26,7 @@ public class AwLayoutSizer {
     // Page scale factor. This is set to zero initially so that we don't attempt to do a layout if
     // we get the content size change notification first and a page scale change second.
     private double mPageScaleFactor = 0.0;
+    private double mLastMeasuredPageScaleFactor = 0.0;
 
     // Whether to postpone layout requests.
     private boolean mFreezeLayoutRequests;
@@ -40,6 +41,7 @@ public class AwLayoutSizer {
     public interface Delegate {
         void requestLayout();
         void setMeasuredDimension(int measuredWidth, int measuredHeight);
+        void setAutoResizeMode(boolean enabled, int widthDip);
     }
 
     /**
@@ -150,12 +152,10 @@ public class AwLayoutSizer {
         int contentHeightPix = (int) (mContentHeightCss * mPageScaleFactor * mDIPScale);
         int contentWidthPix = (int) (mContentWidthCss * mPageScaleFactor * mDIPScale);
 
+        mLastMeasuredPageScaleFactor = mPageScaleFactor;
+
         // Always use the given size unless unspecified. This matches WebViewClassic behavior.
         mWidthMeasurementIsFixed = (widthMode != MeasureSpec.UNSPECIFIED);
-        // Freeze the height if an exact size is given by the parent or if the content size has
-        // exceeded the maximum size specified by the parent.
-        // TODO(mkosiba): Actually we'd like the reduction in content size to cause the WebView to
-        // shrink back again but only as a result of a page load.
         mHeightMeasurementIsFixed = (heightMode == MeasureSpec.EXACTLY) ||
             (heightMode == MeasureSpec.AT_MOST && contentHeightPix > heightSize);
 
@@ -177,4 +177,27 @@ public class AwLayoutSizer {
 
         mDelegate.setMeasuredDimension(measuredWidth, measuredHeight);
     }
+
+    public void onSizeChanged(int w, int h, int ow, int oh) {
+        // Both dimensions are explicitly specified by the partent view, no need for autosizing as
+        // the content size doesn't influence the view size.
+        if (mWidthMeasurementIsFixed && mHeightMeasurementIsFixed ||
+                mLastMeasuredPageScaleFactor == 0) {
+            mDelegate.setAutoResizeMode(false, 0);
+            return;
+        }
+
+        final double dipAndPageScale = mLastMeasuredPageScaleFactor * mDIPScale;
+        final int contentWidthPix = (int) (mContentWidthCss * dipAndPageScale);
+
+        int widthDip = (int) (w / dipAndPageScale);
+
+        // Make sure that we don't introduce rounding errors if the viewport is to be exactly as
+        // wide as the contents.
+        if (w == contentWidthPix) {
+            widthDip = mContentWidthCss;
+        }
+
+        mDelegate.setAutoResizeMode(true, widthDip);
+    }
 }