Workaround for blacklist KHR_blend_equation_advanced on ARM GPU

ARM driver will check the fragment shader compatiblity for KHR_blend_equation_advanced even if blending is disabled.
Workaround: Set blending equation to any basic equation when we disable blending.
https://code.google.com/p/skia/issues/detail?id=3943

BUG=skia:3943

Review URL: https://codereview.chromium.org/1216963004
diff --git a/src/gpu/gl/GrGLCaps.cpp b/src/gpu/gl/GrGLCaps.cpp
index 539212c..22ad057 100644
--- a/src/gpu/gl/GrGLCaps.cpp
+++ b/src/gpu/gl/GrGLCaps.cpp
@@ -888,8 +888,7 @@
     // for now until its own blacklists can be updated.
     if (kAdreno4xx_GrGLRenderer == ctxInfo.renderer() ||
         kIntel_GrGLDriver == ctxInfo.driver() ||
-        kChromium_GrGLDriver == ctxInfo.driver() ||
-        kARM_GrGLVendor == ctxInfo.vendor()) {
+        kChromium_GrGLDriver == ctxInfo.driver()) {
         return;
     }
 
@@ -922,6 +921,10 @@
         fAdvBlendEqBlacklist |= (1 << kColorDodge_GrBlendEquation) |
                                 (1 << kColorBurn_GrBlendEquation);
     }
+    if (kARM_GrGLVendor == ctxInfo.vendor()) {
+        // Blacklist color-burn on ARM until the fix is released.
+        fAdvBlendEqBlacklist |= (1 << kColorBurn_GrBlendEquation);
+    }
 }
 
 namespace {