Plumb gesture source value through Blink.

content/renderer/input/input_handler_proxy.cc

 // Copyright 2013 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.
 
 #include "content/renderer/input/input_handler_proxy.h"
 
 #include <algorithm>
 
 #include "base/auto_reset.h"
 #include "base/command_line.h"
@@ skipping 482 matching lines @@
   input_handler_->ScrollEnd();
   if (!gesture_scroll_on_impl_thread_)
     return DID_NOT_HANDLE;
   gesture_scroll_on_impl_thread_ = false;
   return DID_HANDLE;
 }
 
 InputHandlerProxy::EventDisposition InputHandlerProxy::HandleGestureFlingStart(
     const WebGestureEvent& gesture_event) {
   cc::InputHandler::ScrollStatus scroll_status;
-
   if (gesture_event.sourceDevice == blink::WebGestureDeviceTouchpad) {

[tdresser, 2015/10/14 15:14:20]

This might read a bit better as a switch statement now, but I don't feel
strongly about it.

[wjmaclean, 2015/10/14 15:55:09]

Done.

     if (gesture_event.data.flingStart.targetViewport) {
       scroll_status = input_handler_->RootScrollBegin(
           cc::InputHandler::NON_BUBBLING_GESTURE);
     } else {
       scroll_status = input_handler_->ScrollBegin(
           gfx::Point(gesture_event.x, gesture_event.y),
           cc::InputHandler::NON_BUBBLING_GESTURE);
     }
-  } else {
+  } else if (gesture_event.sourceDevice == blink::WebGestureDeviceTouchscreen) {
     if (!gesture_scroll_on_impl_thread_)
       scroll_status = cc::InputHandler::SCROLL_ON_MAIN_THREAD;
     else
       scroll_status = input_handler_->FlingScrollBegin();
+  } else {  // sourceDevice == blink::WebGestureDeviceUninitialazed.
+    NOTREACHED();
+    return DID_NOT_HANDLE;
   }
 
 #ifndef NDEBUG
   expect_scroll_update_end_ = false;
 #endif
 
   switch (scroll_status) {
     case cc::InputHandler::SCROLL_STARTED: {
       if (gesture_event.sourceDevice == blink::WebGestureDeviceTouchpad)
         input_handler_->ScrollEnd();
@@ skipping 477 matching lines @@
   TRACE_EVENT2("input",
                "InputHandlerProxy::scrollBy",
                "x",
                clipped_increment.width,
                "y",
                clipped_increment.height);
 
   bool did_scroll = false;
 
   switch (fling_parameters_.sourceDevice) {
+    case blink::WebGestureDeviceUninitialized:
+      NOTREACHED();
+      break;

[tdresser, 2015/10/14 15:14:20]

We generally put exceptional cases at the end of switch statements.

[wjmaclean, 2015/10/14 15:55:09]

Done.

     case blink::WebGestureDeviceTouchpad:
       did_scroll = TouchpadFlingScroll(clipped_increment);
       break;
     case blink::WebGestureDeviceTouchscreen: {
       clipped_increment = ToClientScrollIncrement(clipped_increment);
       cc::InputHandlerScrollResult scroll_result = input_handler_->ScrollBy(
           fling_parameters_.point, clipped_increment);
       HandleOverscroll(fling_parameters_.point, scroll_result);
       did_scroll = scroll_result.did_scroll;
     } break;
   }
 
   if (did_scroll) {
     fling_parameters_.cumulativeScroll.width += clipped_increment.width;
     fling_parameters_.cumulativeScroll.height += clipped_increment.height;
   }
 
   // It's possible the provided |increment| is sufficiently small as to not
   // trigger a scroll, e.g., with a trivial time delta between fling updates.
   // Return true in this case to prevent early fling termination.
   if (std::abs(clipped_increment.width) < kScrollEpsilon &&
       std::abs(clipped_increment.height) < kScrollEpsilon)
     return true;
 
   return did_scroll;
 }
 
 }  // namespace content