Add a WebView.zoomBy API.

The WebView has zoomIn/zoomOut APIs which zoom in/out by a fixed
amount. This adds a more flexible API.

BUG: 13399510
Change-Id: Ia505048d5b1c48f9a3ff1c4ce7129ed2f55804f8

api/current.txt

@@ -36700,6 +36700,7 @@ package android.webkit {
     method public void setWebViewClient(android.webkit.WebViewClient);
     method public deprecated boolean showFindDialog(java.lang.String, boolean);
     method public void stopLoading();
+    method public boolean zoomBy(float);
     method public boolean zoomIn();
     method public boolean zoomOut();
     field public static final java.lang.String SCHEME_GEO = "geo:0,0?q=";

core/java/android/webkit/WebView.java

@@ -1944,6 +1944,23 @@ public class WebView extends AbsoluteLayout
         return mProvider.canZoomOut();
     }
 
+    /**
+     * Performs a zoom operation in this WebView.
+     *
+     * @param zoomFactor the zoom factor to apply. The zoom factor will be clamped to the Webview's
+     * zoom limits. This value must be in the range 0.01 to 100.0 inclusive.
+     *
+     * @return false if no zoom changes, true otherwise.
+     */
+    public boolean zoomBy(float zoomFactor) {
+        checkThread();
+        if (zoomFactor < 0.01)
+            throw new IllegalArgumentException("zoomFactor must be greater than 0.01.");
+        if (zoomFactor > 100.0)
+            throw new IllegalArgumentException("zoomFactor must be less than 100.");
+        return mProvider.zoomBy(zoomFactor);
+    }
+
     /**
      * Performs zoom in in this WebView.
      *

core/java/android/webkit/WebViewProvider.java

@@ -238,6 +238,8 @@ public interface WebViewProvider {
 
     public boolean canZoomOut();
 
+    public boolean zoomBy(float zoomFactor);
+
     public boolean zoomIn();
 
     public boolean zoomOut();