Add captureLayers function to capture a layer and its children.

The captureLayers function gets a root layer as its argument.
It will capture the content for that layer and its descendants. The
capture will set the root layer's transform back to (0, 0).

Test: Transaction_test ScreenCaptureTest
Change-Id: I84fb66a65cd91434cddc99506b1924cf9f950935
diff --git a/services/surfaceflinger/RenderArea.cpp b/services/surfaceflinger/RenderArea.cpp
new file mode 100644
index 0000000..6225df1
--- /dev/null
+++ b/services/surfaceflinger/RenderArea.cpp
@@ -0,0 +1,34 @@
+#include "RenderArea.h"
+
+namespace android {
+
+/*
+ * Checks that the requested width and height are valid and updates them to the render area
+ * dimensions if they are set to 0
+ */
+status_t RenderArea::updateDimensions() {
+    // get screen geometry
+
+    uint32_t width = getWidth();
+    uint32_t height = getHeight();
+
+    if (mRotationFlags & Transform::ROT_90) {
+        std::swap(width, height);
+    }
+
+    if ((mReqWidth > width) || (mReqHeight > height)) {
+        ALOGE("size mismatch (%d, %d) > (%d, %d)", mReqWidth, mReqHeight, width, height);
+        return BAD_VALUE;
+    }
+
+    if (mReqWidth == 0) {
+        mReqWidth = width;
+    }
+    if (mReqHeight == 0) {
+        mReqHeight = height;
+    }
+
+    return NO_ERROR;
+}
+
+} // namespace android
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