Add WebView API for smoothScroll

Source/web/WebViewImpl.cpp

Index: Source/web/WebViewImpl.cpp
diff --git a/Source/web/WebViewImpl.cpp b/Source/web/WebViewImpl.cpp
index bede818efbcccedd50386be4fa949b12950d608d..4ad025eea0104632a345d362dd70c03b2c3ec5f4 100644
--- a/Source/web/WebViewImpl.cpp
+++ b/Source/web/WebViewImpl.cpp
@@ -2874,6 +2874,17 @@ bool WebViewImpl::scrollFocusedNodeIntoRect(const WebRect& rectInViewport)
     return false;
 }
 
+void WebViewImpl::smoothScroll(int targetX, int targetY, long durationMs)
+{
+    LocalFrame* frame = page()->mainFrame() && page()->mainFrame()->isLocalFrame()

[dcheng, 2015/07/28 18:50:14]

Who calls this? Will this be covered by a test on the waterfall so we'll know to
fix this later for OOPI?

[aelias_OOO_until_Jul13, 2015/07/28 19:00:21]

Actually, why is this code here at all?  The code below doesn't use the frame. 
startPageScaleFactor doesn't rely on it either.

[hush (inactive), 2015/07/28 19:18:11]

I was copying the logic of WebViewImpl::scrollFocusedNodeIntoRect. I initially
thought scrollFocusedNodeIntoRect does not need frame either, simply using it as
a way to determine valid status. Sorry I missed the part that the frame is used
for retrieving the focused element.
Anyways, I will remove this block.

dcheng@:
This api will eventually be called by Android WebView to implement
pageUp/pageDown.
The callpath is like WebView#pageUp -> ContentViewCore->SmoothScroll ->
WebContents->SmoothScroll -> IPC to blink InputMsg_SmoothScroll ->
render_view_impl->SmoothScroll
I have another CL in progress here https://codereview.chromium.org/1251323002/

+        ? page()->deprecatedLocalMainFrame() : 0;
+    if (!frame || !frame->view())
+        return;
+
+    IntPoint targetPosition(targetX, targetY);
+    startPageScaleAnimation(targetPosition, false, pageScaleFactor(), (double)durationMs / 1000);
+}
+
 void WebViewImpl::computeScaleAndScrollForFocusedNode(Node* focusedNode, bool zoomInToLegibleScale, float& newScale, IntPoint& newScroll, bool& needAnimation)
 {
     focusedNode->document().updateLayoutIgnorePendingStylesheets();