Update from https://crrev.com/320343

sdch/README.chromium

Index: sdch/README.chromium
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+The linux directory contains a config.h generated from a run of configure on
+Ubuntu 10.04.1 LTS x86_64, with VCDIFF_USE_BLOCK_COMPARE_WORDS manually
+changed to match the $host_cpu test in configure.
+
+The mac directory contains a config.h generated from a run of configure on a
+Mac, with VCDIFF_USE_BLOCK_COMPARE_WORDS manually changed to match the
+$host_cpu test in configure.
+
+The ios directory contains a config.h generated from a run of configure
+--host=arm-apple-darwin10 on a Mac with the following environment variables:
+  CC=/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/gcc-4.2 -x c -arch armv6
+  CFLAGS=-mno-thumb -miphoneos-version-min=4.2
+  CPPFLAGS=-isysroot /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.3.sdk
+  CXX=/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/gcc-4.2 -x c++ -arch armv6
+  CXXFLAGS=-mno-thumb -miphoneos-version-min=4.2
+
+The win directory contains a config.h that forwards to one provided with
+open-vcdiff. We have this to avoid putting open-vcdiff's minimal stdint.h hack
+into our include path.