Revert of Remove SkThread.h, include SkMutex.h or SkAtomics.h as appropriate.

Revert of Remove SkThread.h, include SkMutex.h or SkAtomics.h as appropriate. (patchset #4 id:60001 of https://codereview.chromium.org/1215393002/)

Reason for revert:
Breaking the roll.

E.g. on android_chromium_gn_compile_dbg:

FAILED: /b/build/goma/gomacc ../../third_party/android_tools/ndk/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/bin/arm-linux-androideabi-g++ -MMD -MF obj/skia/ext/libskia.SkMemory_new_handler.o.d -DV8_DEPRECATION_WARNINGS -DCLD_VERSION=1 -DENABLE_NOTIFICATIONS -DENABLE_BROWSER_CDMS -DENABLE_PRINTING=1 -DENABLE_BASIC_PRINTING=1 -DDONT_EMBED_BUILD_METADATA -DUSE_OPENSSL=1 -DUSE_OPENSSL_CERTS=1 -DNO_TCMALLOC -DDISABLE_NACL -DENABLE_CONFIGURATION_POLICY -DENABLE_SUPERVISED_USERS=1 -DENABLE_AUTOFILL_DIALOG=1 -DUSE_PROPRIETARY_CODECS -DV8_USE_EXTERNAL_STARTUP_DATA -DVIDEO_HOLE=1 -DMOBILE_SAFE_BROWSING -DSAFE_BROWSING_SERVICE -DCHROMIUM_BUILD -D_FILE_OFFSET_BITS=64 -DANDROID -DHAVE_SYS_UIO_H -DCOMPONENT_BUILD -D__GNU_SOURCE=1 -D_DEBUG -DDYNAMIC_ANNOTATIONS_ENABLED=1 -DWTF_USE_DYNAMIC_ANNOTATIONS=1 -DSKIA_IMPLEMENTATION=1 -DSK_ARM_HAS_OPTIONAL_NEON -DSK_GAMMA_APPLY_TO_A8 -DSK_GAMMA_EXPONENT=1.4 -DSK_GAMMA_CONTRAST=0.0 -DSK_DEFAULT_FONT_CACHE_LIMIT=1048576 -DSK_IGNORE_LINEONLY_AA_CONVEX_PATH_OPTS -DSKIA_DLL -DGR_GL_IGNORE_ES3_MSAA=0 -DSK_SUPPORT_GPU=1 -DSK_BUILD_FOR_ANDROID -DUSE_CHROMIUM_SKIA -DXML_STATIC -I../.. -Igen -I../../third_party/skia/include/private -I../../third_party/skia/src/core -I../../third_party/skia/src/image -I../../third_party/skia/src/opts -I../../third_party/skia/src/pdf -I../../third_party/skia/src/ports -I../../third_party/skia/src/sfnt -I../../third_party/skia/src/utils -I../../third_party/skia/src/lazy -I../../skia/config -I../../skia/ext -I../../third_party/skia/include/c -I../../third_party/skia/include/config -I../../third_party/skia/include/core -I../../third_party/skia/include/effects -I../../third_party/skia/include/images -I../../third_party/skia/include/lazy -I../../third_party/skia/include/pathops -I../../third_party/skia/include/pdf -I../../third_party/skia/include/pipe -I../../third_party/skia/include/ports -I../../third_party/skia/include/utils -I../../third_party/skia/include/gpu -I../../third_party/skia/src/gpu -I../../third_party/zlib -I../../third_party/expat/files/lib -I../../third_party/freetype-android/include -I../../third_party/freetype-android/src/include -I../../third_party/android_tools/ndk/sources/android/cpufeatures -fno-strict-aliasing -march=armv7-a -mfloat-abi=softfp -mtune=generic-armv7-a -mthumb -mthumb-interwork -fno-tree-sra -fno-caller-saves -funwind-tables -fPIC -pipe -ffunction-sections -funwind-tables -fno-short-enums -finline-limit=64 -mfpu=vfpv3-d16 -isystem../../third_party/android_tools/ndk/sources/cxx-stl/llvm-libc++/libcxx/include -isystem../../third_party/android_tools/ndk/sources/cxx-stl/llvm-libc++abi/libcxxabi/include -isystem../../third_party/android_tools/ndk/sources/android/support/include -fvisibility=hidden --sysroot=/b/build/slave/android_chromium_gn/build/src/third_party/android_tools/ndk/platforms/android-16/arch-arm -Os -fdata-sections -ffunction-sections -fomit-frame-pointer -g1 -Wno-format -Wendif-labels -Werror -Wno-missing-field-initializers -Wno-unused-parameter -Wno-psabi -Wno-extra -Wno-ignored-qualifiers -Wno-type-limits -Wno-unused-local-typedefs -fno-threadsafe-statics -fvisibility-inlines-hidden -std=gnu++11 -fno-rtti -fno-exceptions -Wno-deprecated -Wno-narrowing -Wno-literal-suffix -Wno-error=c++0x-compat -Wno-non-virtual-dtor -Wno-sign-promo -c ../../skia/ext/SkMemory_new_handler.cpp -o obj/skia/ext/libskia.SkMemory_new_handler.o
../../skia/ext/SkMemory_new_handler.cpp:12:52: fatal error: third_party/skia/include/core/SkThread.h: No such file or directory
 #include "third_party/skia/include/core/SkThread.h"

Original issue's description:
> Remove SkThread.h, include SkMutex.h or SkAtomics.h as appropriate.
> 
> SkThread.h doesn't do anything anymore execept include those two,
> and thankfully, it doesn't seem to be mentioned outside Skia.
> 
> No public API changes.
> TBR=reed@google.com
> 
> BUG=skia:
> 
> Committed: https://skia.googlesource.com/skia/+/c50acf2321d7a934c80d754e9cbe936dfb8eb4cc

TBR=mtklein@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Committed: https://skia.googlesource.com/skia/+/02802f64ea0b1fc9223386328a95280b74092c94

[jvanverth1, 2015-07-02 13:42:18]

Created Revert of Remove SkThread.h, include SkMutex.h or SkAtomics.h as
appropriate.

[commit-bot: I haz the power, 2015-07-02 13:42:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1214603003/1

[commit-bot: I haz the power, 2015-07-02 13:42:53]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/02802f64ea0b1fc9223386328a95280b74092c94