Various minor cross-platform changes

src/gpu/GrGpu.cpp

Index: src/gpu/GrGpu.cpp
diff --git a/src/gpu/GrGpu.cpp b/src/gpu/GrGpu.cpp
index 6a1c1dd5c95994460e4e478ada6c61024a44d8e2..b86077848a7b076ff0cd62203bf7a5fadfcbf55f 100644
--- a/src/gpu/GrGpu.cpp
+++ b/src/gpu/GrGpu.cpp
@@ -272,6 +272,7 @@ bool GrGpu::getReadPixelsInfo(GrSurface* srcSurface, int width, int height, size
 
     return true;
 }
+
 bool GrGpu::getWritePixelsInfo(GrSurface* dstSurface, int width, int height, size_t rowBytes,
                                GrPixelConfig srcConfig, DrawPreference* drawPreference,
                                WritePixelTempDrawInfo* tempDrawInfo) {
@@ -279,6 +280,11 @@ bool GrGpu::getWritePixelsInfo(GrSurface* dstSurface, int width, int height, siz
     SkASSERT(tempDrawInfo);
     SkASSERT(kGpuPrefersDraw_DrawPreference != *drawPreference);
 
+    if (GrPixelConfigIsCompressed(dstSurface->desc().fConfig) &&
+        dstSurface->desc().fConfig != srcConfig) {
+        return false;
+    }
+
     if (this->caps()->useDrawInsteadOfPartialRenderTargetWrite() &&
         SkToBool(dstSurface->asRenderTarget()) &&
         (width < dstSurface->width() || height < dstSurface->height())) {
@@ -332,6 +338,10 @@ bool GrGpu::writePixels(GrSurface* surface,
                         int left, int top, int width, int height,
                         GrPixelConfig config, const void* buffer,
                         size_t rowBytes) {
+    if (!buffer) {
+        return false;
+    }
+
     this->handleDirtyContext();
     if (this->onWritePixels(surface, left, top, width, height, config, buffer, rowBytes)) {
         fStats.incTextureUploads();