Remove use of private SkBlurMask.h

This also makes a use of src/core/SkTraceEventCommon.h explicit.

These are small steps toward removing Skia's src/core from
the hwui include search path.

Change-Id: I4fe843a4e44a675748bfe2cef329202eb4dab7bf
Bug: skia:13983
diff --git a/libs/hwui/Properties.cpp b/libs/hwui/Properties.cpp
index b0896da..33c9eac 100644
--- a/libs/hwui/Properties.cpp
+++ b/libs/hwui/Properties.cpp
@@ -21,7 +21,7 @@
 #ifdef __ANDROID__
 #include "HWUIProperties.sysprop.h"
 #endif
-#include "SkTraceEventCommon.h"
+#include "src/core/SkTraceEventCommon.h"
 
 #include <algorithm>
 #include <cstdlib>
diff --git a/libs/hwui/jni/MaskFilter.cpp b/libs/hwui/jni/MaskFilter.cpp
index 048ce02..cbd4520 100644
--- a/libs/hwui/jni/MaskFilter.cpp
+++ b/libs/hwui/jni/MaskFilter.cpp
@@ -1,6 +1,5 @@
 #include "GraphicsJNI.h"
 #include "SkMaskFilter.h"
-#include "SkBlurMask.h"
 #include "SkBlurMaskFilter.h"
 #include "SkBlurTypes.h"
 #include "SkTableMaskFilter.h"
@@ -11,6 +10,13 @@
     }
 }
 
+// From https://skia.googlesource.com/skia/+/d74c99a3cd5eef5f16b2eb226e6b45fe523c8552/src/core/SkBlurMask.cpp#28
+static constexpr float kBLUR_SIGMA_SCALE = 0.57735f;
+
+static float convertRadiusToSigma(float radius) {
+    return radius > 0 ? kBLUR_SIGMA_SCALE * radius + 0.5f : 0.0f;
+}
+
 class SkMaskFilterGlue {
 public:
     static void destructor(JNIEnv* env, jobject, jlong filterHandle) {
@@ -19,7 +25,7 @@
     }
 
     static jlong createBlur(JNIEnv* env, jobject, jfloat radius, jint blurStyle) {
-        SkScalar sigma = SkBlurMask::ConvertRadiusToSigma(radius);
+        SkScalar sigma = convertRadiusToSigma(radius);
         SkMaskFilter* filter = SkMaskFilter::MakeBlur((SkBlurStyle)blurStyle, sigma).release();
         ThrowIAE_IfNull(env, filter);
         return reinterpret_cast<jlong>(filter);
@@ -34,7 +40,7 @@
             direction[i] = values[i];
         }
 
-        SkScalar sigma = SkBlurMask::ConvertRadiusToSigma(radius);
+        SkScalar sigma = convertRadiusToSigma(radius);
         SkMaskFilter* filter =  SkBlurMaskFilter::MakeEmboss(sigma,
                 direction, ambient, specular).release();
         ThrowIAE_IfNull(env, filter);