dd readPixels to SkImage

patch from issue 789673007 at patchset 1 (http://crrev.com/789673007#ps1)

BUG=skia:

Review URL: https://codereview.chromium.org/793723002
Change how SkDebugf is sent to stdout on Android.

Previously, a function was called using dlsym in skia_launcher.

Add a static initializer that changes the setting, and include that for
the tools we automate for testing.

Also only do va_copy if we actually use it.

BUG=skia:2454

Review URL: https://codereview.chromium.org/753543003
Gradient shaders: make fPtsToUnit const, pre-cache getType().

This prevents races when calling fPtsToUnit.getType() from multiple threads.

This introduces a small amount of redundant code in SkTwoPointRadialGradient,
but it's probably optimized together into no extra run-time work.

BUG=437511

Review URL: https://codereview.chromium.org/793763003
Include SkTypes.h from SkDynamicAnnotations.h

This allows us to control SK_DYNAMIC_ANNOTATIONS_ENABLED by Sk*Config.h files.
This is a no-op today, because we control it from the compiler command line.

BUG=430815

Review URL: https://codereview.chromium.org/787003003
Rebaseline.

All these images barely differ.

TBR=bsalomon

BUG=skia:

Review URL: https://codereview.chromium.org/795673002