SnapManager implementation using V8 Extras - {WIP}

Scroll snap manager implemented on main-thread and integrated using V8 Extras

Use with following flags:
--disable-threaded-scrolling  --enable-blink-features=CSSScrollSnapPoints,ScrollCustomization


Requires main-thread scroll customization: https://crrev.com/1236913004/

Requires the following snippet patched in chromium:
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -1520,6 +1520,12 @@
     # Compile d8 for the host toolset.
     'v8_toolset_for_d8': 'host',
 
+    # Add the streams V8 extension to the snapshot
+    'v8_extra_library_files': [
+ '../third_party/WebKit/Source/core/page/scrolling/snap/SnapManager.js',
+    ],
+
CQ_EXTRA_TRYBOTS=tryserver.chromium.perf:linux_perf_bisect;tryserver.chromium.perf:mac_10_10_perf_bisect;tryserver.chromium.perf:win_perf_bisect;tryserver.chromium.perf:android_nexus5_perf_bisect

[majidvp, 2015-09-11 20:13:01]

On 2015/09/11 20:08:48, majidvp wrote:

domenic@: this is my initial snappoints integration using V8 Extras. In

The V8 extra's integration happens mostly in 
Source/core/page/scrolling/snap/SnapManager.cpp

Can you please take a look and let me know if this makes sense to you?

The Javascript code is written using vanilla JS and it does not do anything
to be robust against page code. But I don't think that is important at this 
stage. See:
Source/core/page/scrolling/snap/SnapManager.js