Fix Android back button behavior
Pressing the back button should call mServoView.goBack if possible.
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- Add sysroot path to environment variable 'CPPFLAGS':
When checking C preprocessor, the 'configure' script of libbacktrace uses 'CPPFLAGS' rather than 'CFLAGS' and doesn't get the correct search path. (#15758)
This check passes on Linux because the '/lib/cpp' fallback is available there.
- Introduce CMake toolchain file for Android cross compiling:
CMake needs several variables [1] to cross compile for Android.
It works (accidentally) on Linux because cmake-rs sets compilers correctly and binutils for Linux & Android are pretty much the same.
[1] https://cmake.org/cmake/help/v3.7/manual/cmake-toolchains.7.html#cross-compiling-for-android-with-the-ndk
Add very simple Android browser page load support
I've long had this set of private patches that enables actually demoing Servo on Android without having the device connected, but they're a bit hackish due to some current limitations in our windowing toolkit library. I'm considering committing them, though, as it makes the resulting APK *actually* somewhat usable.
Thoughts / r? @mbrubeck
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