Adds UMA for slow and fast back/forward WKWebController navigations.
Adds new UMA histogram: Navigation.IOSWKWebViewSlowFastBackForward to
track the slow/fast back and forward navigations. Fast navigations are
navigations through WKBackForwardList.
Avoid unnecessary byte-swapping in blink's SerializedScriptValue.
For historical reasons, SerializedStringValue byte-swaps its buffer when
serializing to a string. This CL removes the unnecessary flipping for
current values, and sets up a legacy deserialization code path, so
byte-swapped SSVs can still be read correctly.
Remove explicit -fomit_frame_pointer from ARM 32-bit builds.
-fomit_frame_pointer causes the assembly generated from SkEdge::setLine
to trigger a CPU errata in ARM A12/A17 devices, so we are temporarily
removing the flag until the toolchain can be fixed to avoid that.
Replace requirePageReconstruction with setCustomUserAgent
WKWebView provides a property: customUserAgent that we can use to
change the user agent associated with the web view, which means that we
don't have to requirePageConstruction anymore when user agent changes.
After applying this change, I observed that it's becoming significantly
faster to navigate between desktop and mobile pages during back and
forward navigations.