ios fixes

skia_ios.mm
Get the app's Documents directory and pass use it to set the resource path.
This is a quick hack which will be replaced by a new application that is
a tiny shim around a command line tool.

SkImageEncoder.h
SkForceLinking.cpp
SkImageDecoder_CG.cpp
Add support for FORCE_LINKING so iOS sees the PNG encoder and others.

SkFloatBits.cpp
SkPoint.cpp
Handle denormalized numbers that are floored by the iOS ARM processor.

SkImageDecoder_iOS.mm
Remove empty encoder factory.

SkTouchGesture.cpp
Return early on empty state on touch rather than aborting (crashing)

JpegTest.cpp
Hal via stackoverflow.com says partial jpegs can be gray as well.

skia_test.cpp
Remove crash handler call for now to avoid link failure.

OverwriteLine.h
Remove fancy line overwrite for iOS.

Resources.cpp
Add interface to set resource directory based on runtime query.

BUG=skia:2736 skia:2737 skia:2738
R=reed@google.com, halcanary@google.com, mtklein@google.com, tfarina@chromium.org

Author: caryclark@google.com

Review URL: https://codereview.chromium.org/373383003
diff --git a/src/core/SkMathPriv.h b/src/core/SkMathPriv.h
index f93ab61..e997045 100644
--- a/src/core/SkMathPriv.h
+++ b/src/core/SkMathPriv.h
@@ -10,6 +10,12 @@
 
 #include "SkMath.h"
 
+#ifdef SK_BUILD_FOR_IOS
+// The iOS ARM processor discards small denormalized numbers to go faster.
+// Algorithms that rely on denormalized numbers need alternative implementations.
+#define SK_DISCARD_DENORMALIZED_FOR_SPEED
+#endif
+
 /** Returns -1 if n < 0, else returns 0
  */
 #define SkExtractSign(n)    ((int32_t)(n) >> 31)